Le Plantule Della Flora Trapanese

Summary

Secondary wood growth in both a ♂ and a ♀ plant of Schinus Molle has been studied in Bari, Puglia.

The bulk of the secondary wood has been found to be made up of substitution fibres full of starch grains, which it would be more appropriate to call fusiform wood parenchyma cells (according to the « Glossary of Terms Used in Describing Woods», in Tropical Woods, N° 36, 1933).

There are no annual rings: the thickening is due to the addition of successive «growth layers», 3 or 4 per year.

The cambium does not undergo any evident resting period, neither in summer nor in winter, but only periods of suspended activity: the periods of suspended activity do not occur simultaneously in the ♂ and ♀ plants, but in different months.

Each period of cambial activity passes through the three stages of initial, maximum, and decreasing intensity and lasts for 2–3–4 months depending on the season and the sex.

Tipically the growing period starts with the deposition of new elements; next follows lignification of these same elements; during the third stage starch grains appear in the fusiform and radial parenchyma cells of the newly formed wood.

During 1952, 4 growth layers have been formed in the ♂ and 3 in the ♀ plant. In general each episode is slower and more diluted in time in the ♀ plant as compared to the ♂ one. A diversity in cambial behaviour as regards spring reawakening, between the two sexes of dioiceous plants had been already observed in Rhamnus Alaternus (De Paolis, 1949); in both species the ♂ plant appears to be more sensitive and more speedy in its reactions than the ♀ one.

The author does not know of any research on cambial activity in S. Molle carried out in Peru, the native land of this species. Comparing its cambial activity as revealed by the present researches with that of other evergreen plants spontaneous in Puglia the existence of an essential difference is demonstrated: while in S. Molle cambial activity is subcontinuous, in the Mediterranean evergreen trees and shrubs so far studied the cambium undergoes two resting periods, one in winter, and a more or less well defined one in summer. Moreover cambial activity in S. Molle can be taken as continuous if the plants of both sexes are considered, owing to their asinchronism (the same phenomenon happens in flowering times). This lack of a well defined growth cycle corresponds to a similar lack of a well defined seasonal cycle in the climate of the interandine Peruvian valleys, the original habitat of S. Molle, where the mean temperatures of the coldest months vary from 5,8° C to 11,9° C, while those of the hottest months vary from 10,3° C to 15,9° C, with yearly excursions of 4,5 to 5° C.

On the other hand the type of secondary th ckening by successive apposition of wood layers recalls closely that of a group of Mediterranean plants studied in Puglia, that is Ficus carica (Giannuoli, 1949), Olea europaea (Armenise, 1950), and Phillyrea latifolia (Maranò, 1953). In the case of these species the authors had suggested that they belonged, or were related to genera which had originated or developed in regions lacking a well defined seasonal climatic cycle. This hypothesis is confirmed by the fact that S. Molle, a recently imported tropical plant has maintained in our Mediterranean climate not only its original type of secondary thickening, but also its original growth rythm. S. Molle can be considered an experimental test of an hypothesis based so far on the interpretation of observation data.     

Evoluzione Annuale della Cerchia Legnosa in Individui Maschili E Femminili di Ginkyo Biloba L.

Abstract

Wood ring evolution in male and female plants of GINKYO BILOBA L. — A morphological examen of the wood rings in Ginkyo biloba L. has been performed on stem sections from specimens of the Botanical Institute of Florence, on wood samples from the collection of Adriano Fiori and on wood cores extracted from the stem of male and female plants growing in the Botanical Garden of Florence.

At the same time the development of the growth ring has been followed on wood samples tacken off the stems of two adult Ginkyo plants growing in the Botanical Garden of Florence.

All the material which has been studied shows the same characters, that is the frequency of uncomplete crescent-shaped wood rings, and consequently a large degree of eccentricity of the stems, depending not only upon the uncomplete wood rings, but also on the changing width of each ring.

Microscopical analysis has pointed out the presence of false rings, limited by discontinuous late wood, particularly in the female plant. This character has been observed only in a fossil wood of Ginkyo bonesii.

It has not been possible to assers how many rings or crescents are formed during one year. From dating records made on wood cores it seems that more than one ring could differentiate during one year, but the cambium shows a very irregular activity in Ginkyo. The factors which control the formation of false and uncomplete wood rings (wood crescents) are also unknown; their formation possibly depending upon environment conditions.

External factors such as water deficiency probably control cambial activity through auxin production. Larson (1964) has shown that draught causes a decrease in tracheids diameter, and the formation of false growth rings; thus the same causes could have been in action in our plants.

Noteworthy are also the data by Gungkel and Thimann (in Larson 1964) showing that auxin content increases downwards in the shoots of Ginkyo and that the apical bud has a very low auxin production, so that it seems possible that in Ginkyo the leaves supply something which the cortical tissue converts into auxin.

Lastly, the almost continuous growth activity of the cambium in Ginkyo must be pointed out, this causes a great difficulty in checking the beginning and the end of this process along the year. It is any way possible to establish the time of the highest cambial activity, which lies in June-July both in the female and in the male plants.     

L'evoluzione della cerchia legnosa in Quercus Pubescens W. Ein Quercus Ilex L. nel clima di Firenze

Summary

The evolution of the wood ring in Quercus pubescens W. and in Quercus Ilex L. in Florence (from June 1946 to June 1947).

The present study deals with the anatomical characters of the wood ring of Q. pubescens and of Q. Ilex. In both the specimens the wood of the stem and of the young branch has been investigated.

In both plants studied the cambial tissue of the stem starts dividing at the end of April, reaching its maximum activity from May to June.

On the contrary the cambium of the branch differentiates in Q. pubescens a month earlier (18 March-18 April) than in Q. Ilex (18 April-18 May). While in the branch of Q. Ilex a false ring can be seen corresponding to the autumn months, nothing of the kind is found in the branch of Q. pubescens; though it presents a false ring in the stem.

It is difficult to date clearly the period when the cambium stops its activity, but probably it happens at the end of August in the samples of the stem.

The leaf buds of Q. pubescens and of Q. Ilex open during April-May and the young branch is completely developed at the end of June. In both oaks some buds open in autumn, but the small branches are prevented to develop because of the cold.

No comparison can be made between the opening of the buds and the beginning of the cambial activity in the stem and in the branch.

Considering the evolution of these woods and their relationship to climatic factors, we can see that the cambial activity starts during a period of remarkable rainfall and of regular increase of temperature, and stops almost completely at the end of July, when temperature and dryness reach their highest values.

The autumn rainfall would favour again a cambial activity, but the values of the temperature, regularly decreasing, do not allow it.     

Cambial activity and annual rhythm of xylem production of elephant apple tree (<Emphasis Type="Italic">Dillenia indica</Emphasis> Linn.) in relation to phenology and climatic factor growing in sub-tropical wet forest of northeast India

The interrelationship between phenological events, climatic factors, periodicity of cambial activity and seasonal production of xylem was examined in Dillenia indica L. (Dilleniaceae) growing in sub-tropical wet forest of Meghalaya state, India. The reactivation of cambial activity was seen in the first week of May, 15 days after sprouting of new leaves and buds. The activity of cambium and xylem production gradually declined toward December and ceased from January to April end. There was correlation between leaf fall and cambial dormancy. It was evident from the correlation and regression analysis, the relationship between cambial activity, xylem production with climatic factors, the monthly mean minimum temperature plays an important role for the cambial activity and xylem production rather than influence by rainfall and relative humidity in D. indica L. The data were discussed in the light of cambial activity, xylem production and phenological events.     

Genetic studies in dioecious melandrium. I

Sex-linked and sex-influenced inheritance are of interest because of their relation to the still intriguing problem of sex detrmination. Genes involved in the formation of the sex organs are regarded to be sex-determining genes. These genes may be present in all chromosomes including the sex-chromosomes. Other genes present in the sex-chromosomes, but not involved in sex determination, are the sex-linked genes. A mutation for narrow leaves we came across in ourM. ablum material is regarded as a case of sex linkage. Also the certation effect observed inM. album andM. dioicum must have been caused by genes on the sex-chromosomes. In both cases, however, it is not altogether unikekely, that the genes, regarded as sex-linked ones, actually take in the process of sex-determination.Sex-determining genes might influence the effect of other genes, that are therefore called sex-influenced genes. We observed a number of such sex-influenced characters inMelandrium.InM. album, female plants are, on the whole, larger than male plants, having larger stems and leaves. The petals, however, are larger in male plants, except in families with very broad petals. The leaves and petals are narrower in female plants than in male ones, except in families with very broad leaves and families with broad petals, where the difference in shape was no longer present. Usually, slightly more anthocyanin is formed in male plants than in females both in petals and the green parts. More glandular hairs were observed on male plants than on female ones.Insofar the observations were made inM. dioicum the same results were obtained.We regard these phenomena to be an expression of the different physiological conditions in female and in male plants, these conditions being provoked by the sex-determinging genes and more favourable for vegetative growth in female than in male plants.     

Ciclo di Accrescimento E Differenziazione Delle Gemme in Piante Perenni Nel Territorio di Bari

Summary

Growth cycle and buds differentiation in perennial plants growing in Bari's area. — V. The evolution of the wood ring in Rhammus Alaternus L. from December 1946 to March 1949.

In Rhamnus Alaternus L. the cambium awackens in March with the production of an early wood, characterized by large vessels and loose fibers. It keeps on dividing the following months, producing intermediary wood, whose vessels become narrower and narrower. In June the wood ring is almost complete and the cambial activity slows down. In July late wood is formed, with narrow tracheae and highly lignified fibers. From August to February cambial activity is very scarce and irregular, in the wood produced fibers being tangentially compressed.

In a young branch of R. A. cambium becomes suddenly active in February, that is one month before than in the stem, it goes on during the month of March-June, with an evident diminution in the size of the wood elements. This diminution of size instead of being regular, shows some oscillations, expecially during the month of May. In Sept. the cambium starts again dividing, but rather poorly and irregularly, forming some vessels a little wider than the preceeding ones, so that an incomplete false ring is formed only in some points of the branch. As a rule the autumn wood is a typical late wood. This scarce and irregular cambial activity goes on also during Oct.-Dec. In January is more active and forms rather wide vessels in comparison with those formed in the preceeding month. This new formed wood however does not show the characteristics of the early wood of a new ring.

Concluding, the characteristics of the cambial activity of A. R. are

In the stem: 1) March: early wood. 2) March-June: intermediary wood. 3) July: late wood, resting period. 4) At the end of Autumn a scarce production of late wood is sometimes possible.

In the young branch: 1) February: early wood. 2) March-June: intermediary wood, with positive and negative oscillations in the vessels width. 3) At the end of June the late wood is already differentiated. 4) July-August: resting period. 5) Spt.-Juan.: the cambium starts again dividing very scarcely and producing a transition wood between the two rings. This wood can be regarded neither as a true ring nor a false one, it represents rather the last phase of the late wood formation. 6) In the young branch of the female specimen the cambium starts dividing somewhat later than in the male one. 7) The wood ring width does not vary much in relation to the yearly amount of rainfall. The lack of relation between rainfall and ring width is particularly evident in 1948 (a rainy year). The, «Compleasance» of R. A. could show that this species is, in Puglia, in its own habitat. On the other hand it is rather peculiar that R. A. forms only one wood ring during one year, with production of early wood during the spring, and of late wood in the autumn, instead of producing a second autumn ring following a distint summer rest, as could be expected.     

Reproductive isolating mechanisms contributing to asymmetric hybridization in Killifishes (Fundulus spp.)

When species hybridize, one F1 hybrid cross type often predominates. Such asymmetry can arise from differences in a variety of reproductive barriers, but the relative roles and concordance of pre-mating, post-mating prezygotic, and post-zygotic barriers in producing these biases in natural animal populations have not been widely investigated. Here, we study a population of predominantly F1 hybrids between two killifish species (Fundulus heteroclitus and F. diaphanus) in which >95% of F1 hybrids have F. diaphanus mothers and F. heteroclitus fathers (D♀ × H♂). To determine why F. heteroclitus × F. diaphanus F1 hybrids (H♀ × D♂) are so rare, we tested for asymmetry in pre-mating reproductive barriers (female preference and male aggression) at a common salinity (10 ppt) and post-mating, pre-zygotic (fertilization success) and post-zygotic (embryonic development time and hatching success) reproductive barriers at a range of ecologically relevant salinities (0, 5, 10, and 15 ppt). We found that F. heteroclitus females preferred conspecific males, whereas F. diaphanus females did not, matching the observed cross bias in the wild. Naturally rare H♀ × D♂ crosses also had lower fertilization success than all other cross types, and a lower hatching success than the prevalent D♀ × H♂ crosses at the salinity found in the hybrid zone centre (10 ppt). Furthermore, the naturally predominant D♀ × H♂ crosses had a higher hatching success than F. diaphanus crosses at 10 ppt, which may further increase their relative abundance. The present study suggests that a combination of incomplete mating, post-mating pre-zygotic and post-zygotic reproductive isolating mechanisms act in concert to produce hybrid asymmetry in this system.     

Hybridization and F1 backcrosses between two closely related tropical species of sea urchins (genus Echinometra) in Okinawa

Summary

Four species of sea urchins of the genus Echinometra, designated species A, B, C, and D, occur along the coast of Okinawa; they are distinguished by color pattern and other characteristics. The two most distinct species, Echinometra sp. A (Ea) with white-tipped spines and Echinometra sp. D (Ed) with nearly black spines (possibly E. oblonga), were examined for potential hybridization through a series of fertilization experiments and rearing of the resulting hybrids. Fertilization was reciprocally asymmetrical; Ed ova were readily fertilized by sperm of Ea, but less than 20% of the ova of Ea were fertilized by sperm of Ed. Nevertheless, hybrids resulting from crosses in both directions developed normally through larval and juvenile stages to produce sexually mature adults. Larvae of Ed♀×Ea♂ and Ed♂×Ed♀ were larger than those of Ea♂ × Ed♀ and Ea♂ × Ea♀, reflecting the larger eggs of Ed. However, Ea♂×Ea♀ juveniles and later stages, up to maturity, were consistently larger than those of equivalent ages of the other crosses; largest to smallest were Ea♂×Ea♀, Ed♂×Ea♀, Ea♂ × Ed♀, and Ed♂×Ed♀, respectively. Ova and sperm of the hybrids were viable and fertilizable in all combination of crosses, although fertilization of those of Ed♂×Ea♀ hybrids was consistently higher than those of Ea♂ × Ed♀ hybrids. These experiments represent the first reported successful production of hybrid sea urchins with viable gametes. They indicate that reproductive isolation is achieved by prezygotic isolating mechanisms in these two species. Of these mechanisms, gametic incompatibility is probably only partly involved, if at all, and differences in spawning times, habitat segregation, or other factors appear to be important for maintaining reproductive isolation in these closely related species.     

Continuity of Procambium and Anomalous Cambium During Formation of Successive Cambia in Celosia argentea

The development of woody plants is related to the continuity of the procambium and cambium. Whether such a continuity is present in plants with successive cambia, especially in those, where the first cambium is formed outside the primary vascular bundles, has not been analyzed so far. Therefore, we studied the development of vascular meristem in Celosia argentea, in which the first and successive cambial cylinders arise outside the primary bundles and, intriguingly, in the literature are interpreted as developmentally independent structures. Our results showed that in C. argentea, the outermost procambial cells maintain their meristematic characteristics during differentiation of vascular bundles and divide periclinally, forming the zone of procambium-derived cells outside the primary bundles. This zone comprises parenchyma cells bordering the bundles, and a continuous ring of the incipient cambial cells neighboring the primary cortex. Later in the development, the ability to preserve the outermost cells in the cambium undifferentiated is repeated during the formation of successive cylinders of cambia. Together, our results clearly point to the developmental continuity of the procambium and successive cambia in C. argentea, despite their seemingly spatial distinctiveness. We postulate that the mechanism demonstrated in C. argentea is universal and orchestrates the development of successive cambia in other plant species.

     

Florivores on the dioecious shrub Eurya japonica and the preferences and performances of two polyphagous geometrid moths on male and female plants

Flowers of dioecious plants have sexually dimorphic traits that may affect florivore performances, and florivores may have preferences to plant sex that are correlated with their performance on different plant sexes. We investigated the florivory on a polygamodioecious evergreen shrub Eurya japonica in Japan to reveal florivores and their feeding patterns involved in sexually biased florivory on E. japonica flowers. Flowers of E. japonica were infested by lepidopteran and dipteran larvae and hemipteran insects. Lepidopteran larvae were chewers, dipteran larvae were gall makers and hemipteran insects were suckers. Chewed flowers were most frequent among infested flowers. Of florivores, lepidopteran larvae, mostly of Geometridae, were the important florivore that damaged flowers by chewing. Florivores infested male flower buds more often than female flower buds, but only a geometrid larvae Chloroclystis excise, which exclusively uses flower buds, showed the biased infection on male flowers. Rearing experiments for two other geometrid moths which use both leaves and flowers showed that the preference and performance of Ourapteryx nivea that fed mainly leaves did not differ between the plant sexes, whereas the development of Alcis angulifera larvae which fed both leaves and flowers was slower when they fed female than male leaves and flower buds. In addition, A. angulifera larvae fed fewer flower buds on female than on male plants. These results show that the male‐biased florivory on E. japonica trees is attributed mainly to the specialist florivore and also feeding preference for male flowers in an opportunistic florivore that feed both leaves and flowers.     

Sul Dioicismo Di Idesia Polycarpa Maxim

Summary

On the dioecism in idesia polycarpa maxim.

Idesia polycarpa Maxim. is a dioecious species, native of Japan and China. Two specimens have been studied for this research, a ♀ and a ♂ one, growing in the Botanical garden of Siena.

The female plant does not present anomalies in the sex behaviour; the male plant, on the contrary, bears occasionaly some flowers with ovaries, which exceptionally develop into fruits.

In the Botanical Garden of Pisa a case of complete sex inversion has been observed (male into female).

In both the ♀ and the ♂ the first development stage is identical and hermaphrodyte. The flower is tendentially proterandrous, unisexuality being attained only successively.

In the male flowers the pystil degenerates while the pollen mother cells undergo meiosis. The ovary ceases developing farther, at the ovule forming stage from the placentae. The only cellular line which degenerates is the epithelium, which lines the ovary inner surface and extends as far the upper surface of the stygma. The microspores tetrads form contemporarily. The tapetum is of the secretory type.

The stamens degenerates in female flowers at the moment corresponding to the passage from the vegetative to the reproductive stage; i. e. the stamens of the female flowers are not capable to carry out the meiosis. The first cellular layer to be reached by a degeneration process is the tapetum; the second is the archesporial tissue. During the degeneration of these two tissues ovules are developing. The female gamethophyte is of the monomegasporial, normal, eightnucleate type. The fruits born by the female plant are roundish, with 8–30 fertile seeds and 50–65 sterile ones. Thè fruits which are exceptionally born by the male plant are bigger, pear-shaped, and countain 20–40 fertile seeds and 65–85 sterile ones.

The epithelium lining the ovaries undergoes total degeneration in normal male flowers; a partial one in the occasional male flowers which have more or less developed pistils. When only the stygma epithelium degenerates, the ovary produces a higher number of ovules even through the whole style region, so that a style does not form and the ovary does not shut, giving a pear-haped fruit.

A higher number of seeds are therefore produced by such an ovary, not only because the placentae go on producing ovules for a longer period, but because also their stylar region is active in this process. It is evident then, that the stigma plays a very important role in the normal closing of the ovary.

In the cases of partial degeneration, ovules remain vital only where the corresponding epithelium is unaltered. This shows that the epithelium has a great importance in the ovule producing phase of the placentae.

Everything seems to point out that the anthers degeneration is autonomous, owing to its own incapacity to undergo meiosis. On the contrary the suppression of the ovary in the male flower is not autonomous and does not occur in a particular moment of the ovary development, but it coincides with microsporogenesis. The suppressor of the ♀ sex therefore acts through the opposite sex. In a male plant where the anthers happen to degenerate, pystils develop in various degree, even completely.

The flowers of the female plant reache the microsporogenesis stadium about 15 days later than those of the male. The author suggests that this delay may be responsible for the realization of the female sex, checking the normal development of the anthers, probably under the influence of environmental factors. On this base he has tried to explain anomalies in male flowers.     

A Study of the Behaviour of the Australian Field Cricket Teleogryllus commodus (Walker) (Orthoptera: Gryllidae) in the Field and in Habitat Simulations

The behaviour of T. commodus (Walker) in the field and in simulated natural habitats is described. Regular predictable sequences of behaviour are represented by an ethogram. Most behaviour was centred around burrows or sheltered sites. Burrows appeared to be a limiting resource and there may be behavioural dimorphism in ♂ ♂ (burrower and non-burrower strategies). Individuals were found to form gregarious clusters and appeared to be attracted to areas already occupied by crickets. Territorial spacing and other social interactions occurred within these clusters. ♂ ♂ and ♀ ♀ were found to be mobile, and moved continually between sites. The movement of ♂ ♂ and ♀ ♀ between burrows (calling sites) was measured. Adult ♂ ♂ never remained at a burrow for longer than two days. In simulated natural habitats ♂ ♂ moved in response to two factors: first, and most common, as a result of eviction by other ♂ ♂ second, as a response to the absence of ♀ ♀. When cricket density was increased in habitat simulations crickets clustered at calling sites. The adaptive significance of T. commodus behaviour is discussed.     

Osservazioni sul ciclo di sviluppo delle gemme di esemplari mascbili e femminili di Ginkyo biloba L.

Abstract

Observations on the development cycle of the buds of male and female specimens of Ginkyo biloba L. – A study of the buds of long shood and short shoot of male and female Ginkyo biloba L. individuals reveals the following: 1) All the buds of the male individuals are bigger and round in shape while those of the female individuals are smaller and conical. 2) Among individuals of the same sex there are no differences between the buds of long and short shoots except that the latter are always bigger. 3) All the buds, both male and female, show a constant number of buds scales (7–14), embryonic leaves (3–7) and leaf primordia (3–4). 4) The increase in diameters is greater in the male than in the female buds. 5) When opening, the buds of the male short shoots can get as big as 11,5 mm × 11,5 mm and those of the female short shoots 5 mmx4 mm. At this time, the long shoots of both sexes show a less marked differences in size (♂ 5 mm × 5 mm; 9 4 mm × 3,5 mm). 6) The male buds of both long and short shoots are always mixed, that is they are provided with a very small apex and pollen sacs. Only on exceptional cases has sterility been observed. On the other hand female buds are mixed, that is they are provided with a shoot apex and ovules, only in the long shoots of three or more years of age and not always; while the buds of the long shoots are always sterile. 7) Opening of the buds, which in both sexes occurs from the base upwards, takes place at the middle of March in the male and in the first decade of April in the female individuals. 8) The appearence of sex, starting from the base, takes place at an earlier time in male individuals. In fact in the buds of the male short shoots it appears as early as July. In the buds of the female short shoots it appears in October. 9) Pollen cones do not appear at the same time in all the buds of the two types of shoot. They are found in the buds of the short shoots in July, in October in the lateral buds of the long shoots and in November in the terminal buds of the same type of shoots. 10) Ovules appear only in some buds of short shoots three or more year old. They are never present in the long and short shoots one or two year old buds. 11) The dates of appearance of the pollen cones and ovules in our Florentine specimens are exactly the same as those reported by SPRECHER (1907) for the Ginkyo plants growing in Geneva.     

Sex expression, skewed sex ratios, and microhabitat distribution in the dioecious desert moss Syntrichia caninervis (Pottiaceae)

The moss Syntrichia caninervis is the dominant soil bryophyte in a blackbrush (Coleogyne ramosissima) community in the southern Nevada Mojave Desert, with a mean cover of 6.3%. A survey of the 10-ha study site revealed an expressed ramet sex ratio of 14♀ : 1♂ (N = 890), with 85% of ramets not expressing sex over their life span, and an expressed population sex ratio of 40♀ : 2♂ : 1♀♂ (female : male : mixed-sex, N = 89), with 52% of populations not expressing sex. A greater incidence of sex expression was associated with shaded microsites, higher soil moisture content, and taller ramets. Shaded microsites had higher surface soil moisture levels than exposed microsites. In the exposed microhabitat, surface soil moisture was positively correlated with ramet height but not with sex expression. Male ramets and populations were restricted to shaded microhabitats, whereas female ramets and populations were found in both shaded and exposed microhabitats, suggesting gender specialization. The rarity of mature sporophytes, found in 0% of the ramets sampled and in only 3% of the populations, is probably due to the rarity of mixed-sex populations. We hypothesize that mixed-sex populations are rare because of factors relating to male rarity and that the differential cost of sex expression reduces the clonal growth capacity of male individuals.     

Prove DI Degemmazione Nel Pesco E Loro Effetti Sulla Istogenesi della Cerchia Legnosa

Summary

Tests on disbudding and their effects on the histogenesis of the wood ring. In this work the effects of hormonic character which appear during the histogenesis of the wood ring have been studied testing disbudding effects on the peach tree.

Some observations on the consequences due to defoliation are also included.

By removal of the buds, the annual ring shows a greater depth and a more marked uniformity of structure, due to an increased frequency of the vascular elements.

By removal of the leaves, the cambial activity is completely inhibited. These results are attributed to the fact that the leaves, according to the more recent hypotheses, produce the substance which stimulates the formation of the wood elements and the differentiation of the newly formed elements.

This inactive substance, produced by the leaf, would exert its action only when the buds, towards which it is directed, transform it into its active form. The removal of the buds would eliminate the centres of diffusion of the inactive substance and also its centres of activation and concentration for the coming rest period, in view of a new vegetative cycle.

As a conseguence the circulation of the inactive substance is more marked, as it is probably activated by the cambium, and its activity lasts longer, producing in the annual ring those characters peculiar to the spring wood, that is of a season in which the circulation of this substance is at its utmost.     

Sex ratio and sex expression in an urban population of the silver moss,Bryum argenteum Hedw.

ABSTRACT

Introduction. A well-supported pattern among dioicous bryophytes is male rarity. However, few assessments of bryophyte sex ratios have been made across environmental gradients to assess the role of environment in shaping population sex ratios.

Methods. We systematically surveyed 200 shoots from a 20?m² urban population of Bryum argenteum, and regenerated each shoot apex until sex expression occurred (up to 315 days).

Key results. Female shoots outnumbered male shoots 132 to 68, giving a sex ratio of 1.94♀: 1♂. The female bias was found in two transects in higher light environments but not in the third transect, which had a lower light level and an equal sex ratio. Female shoots took longer than male shoots to reach gametangial induction (122 vs. 60 days) and longer to produce 5 inflorescences (120 vs. 80 days). Male shoots produced an average of 10× the total number of inflorescences compared to female shoots (34 vs. 3.5 inflorescences). Despite producing more inflorescences, male plants also produced more regenerant shoots, thus contradicting the prediction that a higher prefertilisation reproductive effort in males trades off with vegetative proliferation. Female plants harboured significantly more associated microbes than male plants.

Conclusions. Our results support the role of light in influencing sex ratios in this species, suggest that trade-offs between reproduction and vegetative growth may not be strong for males, and indicate a potential role of a sex-specific microbiome in influencing sex ratios.     

Attractive Spring-food for willow grouse (Lagopus lagopus subsp. lagopus L.) studied using plant macrofossils and pollen in faeces: a methodological discussion

While macrofossil remains of herbs and flowers have disintegrated beyond identification, pollen survives the digestive process and can be identified, sometimes to species level, and is hence an important tool in determining and reconstructing animal diets.

This study compares macroscopic plant parts and pollen remains in faeces from grouse. While macroscopic remains reflect the quantity of bark, twigs, berries and leaves in the birds' food, the pollen also reflects other food, such as catkins, flower buds with developed pollen, flowers and pollen attached to leaves.

Both techniques reflect that Betula and Salix are the most important food for grouse in early Spring. Pollen analysis shows that later in Spring, after snow-melt, the birds are attracted to different plants, firstly, it is taxa within the Ericales and their fruits from the previous year. The nutrient value of food in periods with more or less snow cover is based on the environmental conditions of the previous year. Later on, different herbs, including insect-pollinated plants rich in nectar/sugar, are recorded in the pollen but are not reflected in the macro study, and are therefore lost in most calculations and not discussed. Nutrient content calculations based on Spring and Summer flowers need to be compared with the environmental and climate conditions of the current year.     

Nuptial Flight in two Ponerine Ants,Pachycondyla Impressa and P. Fauveli,Overlooking Machu Picchu,Peru

We report on a simultaneous nuptial flight of ants of two sympatric ponerine species, Pachycondyla impressa and P. fauveli, on the top of Huayna Picchu (2700 m), Peru. After flying in and landing on the flat, hare rocks of the summit, the conspecific sexuals approached, antennated and mated without any previous female calling behaviour. During one hour of observation, the number of approximately 30 ♂ ♂ and ♀ ♀ Pachycondyla impressa and 70–86 of P. fauveli on the site remained constant because of individuals continuously arriving and leaving. Although nuptial flight seems to be the most common type of mating system in ants, this is one of the very few reports on the occurrence of this behaviour in ponerine species.     

VASCULAR CAMBIUM AND WOOD DEVELOPMENT IN CARBONIFEROUS PLANTS. I. LEPIDODENDRALES

Patterns of activity in the vascular cambium of Carboniferous arborescent lycopods (Paralycopodites and Stigmaria) were studied by analysis of serial tangential sections of the secondary xylem. The analysis assumes that cell patterns in the wood accurately reflect those of the corresponding cambium. An evaluation using indirect evidence indicates that the assumption is valid as far as can be determined from comparison with living plants. The tracheids of the secondary xylem enlarge in a centrifugal pattern, suggesting a progressive enlargement of the fusiform initials. There is no evidence of periodic anticlinal division of these initials, and it is proposed that the increase in cambial circumference was accommodated primarily by an increase in fusiform initial size. In some axes with abundant secondary xylem there is evidence that isolated initials or groups of initials sporadically subdivided to form numerous, spindle-shaped meristematic cells. Some of these cells subsequently developed into typical cambial initials. Tissues presumably formed during the cessation of cambial growth in Lepidodendron and Stigmaria are described; the structure of the tissues is suggestive of a postmeristematic parenchymatous sheath. It is concluded that cambial activity in these arborescent cryptogams was clearly different from that of modern seed plants, further attesting to the distinctive nature of this ancient group.