ANASTOMOSES IN THE VENATION OF GINKGO BILOBA

Arnott , Howard J. (Northwestern U., Evanston, Ill.) Anastomoses in the venation of Ginkgo biloba. Amer. Jour. Bot. 46(6): 405–411. Illus. 1959.—Although the vasculature of the lamina of Ginkgo biloba has been described as open dichotomous and devoid of anastomoses, vein unions were found in a survey of 1065 leaves collected from both long and short shoots of 11 trees. When studied by directing a strong light through the lamina and by clearings, 9.9% of the leaves possessed 1 or more anastomoses. Long shoot-leaves showed 13.4% anastomoses while short shoot-leaves showed 8.2% anastomoses. Multiple anastomoses were found in almost half of the leaves bearing anastomoses. In the 105 leaves having vein unions, 163 anastomoses were counted. These anastomoses could be grouped into 4 types which are easily distinguished by the number of dichotomies involved and by the presence or absence of dichotomies above the point of vein union. Other deviations were found from the “normal” venation pattern; these consisted of unconnected veins, veins anastomosed marginally but unconnected basally, and veins ending a considerable distance from the margin. It was speculated that the anastomoses found in Ginkgo biloba are of a simple, archaic type and are apparently analogous to the anastomoses in the leaves of certain ferns and in the leaflets of various cycads. The evolutionary significance of these anastomoses must be assessed by a broad study of venation patterns in the seed-plants.     

MORPHOLOGY AND DICHOTOMOUS VASCULATURE OF THE LEAF OF KINGDONIA UNIFLORA

Foster , Adriance S. (U. California, Berkeley), and Howard J. Arnott . Morphology and dichotomous vasculature of the leaf of Kingdonia uniflora. Amer. Jour. Bot. 47 (8): 684–698. Illus. 1960.—An intensive study of the nodal anatomy, petiolar vasculature and open dichotomous venation of the leaf of Kingdonia has revealed a type of foliar vascular system of unusual morphological and phylogenetic interest. The vascular supply at the nodal level consists of 4 collateral traces which diverge from a single gap into the sheathing leaf base. This type of nodal anatomy is perhaps primitive, and comparisons are made with the unilacunar nodes and the 2- and 4-parted leaf trace systems characteristic of many angiospermous cotyledons and the foliage leaves of certain woody ranalian genera. The petiole of Kingdonia is vascularized by 2 pairs of bundles which represent the upward continuation of the 4 leaf traces. A transition from an even (4) to an odd (3) number of strands occurs near the point of attachment of the 5, lobed, cuneiform lamina segments to the petiole. Each of the 2 abaxial bundles dichotomizes and the central derivative branches fuse to form a double bundle which enters the base of the median lamina segment. The 2 adaxial petiolar bundles diverge right and left into the bases of the paired lateral segments of the lamina. An analogous type of transition from an even to an odd number of veins occurs in many angiospermous cotyledons which develop a definable mid-vein. But, in Kingdonia, the bundles which enter the bases of the lamina segments give rise to systems of dichotomizing veinlets devoid of “mid-veins.” Although the majority of the terminal veinlets enter the marginal teeth of the lamina segments, “blind” endings, unrelated to the dentations, occur in all the leaves studied. Typically, all of the vein endings in a given lobule of a lamina segment are derived from the same dichotomous vein system. However, in some leaves, a veinlet dichotomizes directly below a sinus and the branches diverge into the marginal regions of 2 separate lobules. The phylogenetic significance of the occurrence of open dichotomous venation in such an herbaceous angiosperm as Kingdonia is briefly discussed. From a purely morphological viewpoint, the Kingdonia type of venation invites direct comparison with the venation of Sphenophyllum, certain ferns or Ginkgo rather than with any of the known reticulate venation patterns of modern angiosperms. Although the foliar venation of Kingdonia may represent the result of evolutionary reversion, the very rare anastomoses which occur seem primitive in type rather than “vestiges” of a former system of closed venation.     

A comparison of venation pattern development in wild type and a homeotic sepaloid petal mutant of Clarkia tembloriensis (Onagraceae)

Vascular system development in sepals, petals, and sepaloid petals was compared in wild-type and crinkled petal mutant plants of Clarkia tembloriensis. Patterns of vascularization in cleared whole mounts were visualized and traced under both brightfield and polarizing illumination. Wild-type sepals exhibited a basipetal pattern of maturation, with tracheary elements maturing relatively rapidly. Mature sepals had three primary veins with numerous secondary veins. In contrast, wild-type petals exhibited an acropetal pattern of maturation, with tracheary elements maturing relatively slowly. The mature petals had only one primary vein with numerous secondary veins. Sepaloid (crinkled) petals combined characteristics of both wild-type sepals and wild-type petals. They exhibited a basipetal pattern of development and a relatively rapid maturation of the tracheary elements characteristic of wild-type sepals. Venation architecture in crinkled petal mutants showed a single primary vein with numerous secondary veins, similar to wild-type petals. The crinkled petal mutant fits the definition of a homeotic mutant in that the petal has assumed characteristics of the sepal. However, homeotic transformation from petal to sepal is incomplete since the crinkled petal still retains many of the characteristics of wild-type petals.     

独叶草叶二叉分枝脉序中网结脉和盲脉的形态学研究

对独叶草营养叶二叉分枝脉序及其中的网结脉和盲脉的形态学研究表明：(1)网结脉中2条完全汇合的与靠近脉中完全分离的叶脉之间未发现任何形式的维管束汇合的中间类型及网结脉中具有不同程度的连接脉退化痕迹的事实表明,网结脉不可能由靠近脉产生,相反,由于网结脉中联结脉的退化而形成开放脉;(2)盲脉是通过伴随着齿退化的达齿脉的退化、网结脉中联结脉的间断、非网结脉由分枝处间断三种方式产生的;(3)越裂片脉的出现及其可以形成网结脉的现象表明独叶草营养叶可能曾具有较为复杂的脉序,这种叶脉也呈现出退化的趋势;(4)独叶草营养叶的二叉分枝脉序可能是一种退化性状,而网结脉的出现可能是这种退化过程中的残留痕迹。     

STRUCTURE AND DEVELOPMENT OF THE PERIANTH IN DOWNINGIA BACIGALUPII

The structure and ontogeny of the calyx and corolla of Downingia bacigalupii Weiler (Campanulaceae; Lobelioideae) were investigated for the purpose of comparing perianth development with previous observations on the floral bract, as well as elucidating the mechanism of development of the zygomorphic, sympetalous corolla. Sepals are uni-traced with a palmate, reticulate venation. They have basal and apical hydathodes, as well as storage tracheids. Sepals show a reduction in size, venation and hydathode number when compared to the bract. The pentamerous, zygomorphic corolla is bilabiate, consisting of a three-lobed adaxial lip and a two-lobed abaxial lip connected by a short tubular region. The constituent petal lobes are also uni-traced and have a reticulate venation, resembling that of the sepal and bract, but lack storage tracheids and hydathodes. Sepals arise in an adaxial to abaxial succession and are initiated in the outer corpus layer of the floral apex. Expansion of the floral apex follows and is accompanied by the establishment of a second tunica layer. Sepals undergo apical, marginal, and intercalary growth accompanied by acropetal differentiation of procambium. The petals arise simultaneously and are initiated in the second tunica layer and the outer corpus cells. After initiation, the petals exhibit a period of apical and marginal growth followed by intercalary growth. Apical growth in petals is less protracted than in sepals, but plate meristem activity is more extensive. The free petal lobes become temporarily fused by an interlocking of marginal epidermal layers, but they separate at anthesis. Zonal growth beneath the originally free lobes forms the tube and lip regions of the sympetalous corolla. Zygomorphy is evident from the time of initiation of petals and is accentuated by later differential growth. Comparative observations of corolla ontogeny in autogamous species of Doumingia indicate that the reduced corollas in these taxa are derived by a simple process of neoteny.     

A COMPARISON OF FLORAL DEVELOPMENT IN WILD TYPE AND A HOMEOTIC SEPALOID PETAL MUTANT OF CLARKIA TEMBLORIENSIS (ONAGRACEAE)

The mature wild type petals of Clarkia tembloriensis consist of a long slender claw and an expanded deltoid-shaped limb. They are pink, with a maroon spot at the base of the limb. Their surface texture is smooth. A variant of petal form, crinkled petal, occurs commonly in several natural populations of C. tembloriensis. The mature crinkled petals are elongated, greenish pink, and possess trichomes. They resemble the mature sepals of C. tembloriensis in general shape, color, and surface texture. Organ initiation and subsequent patterns of development of wild type petals, wild type sepals, and crinkled petals were examined and compared using scanning electron microscopy and allometric growth analysis. Crinkled petals are similar to wild type petals in time and position of primordia initiation, and in size and shape at inception. Crinkled petals are similar to wild type sepals in pattern of allometric growth. The crinkled petal mutant fits the broad definition of a homeotic mutant in that the petal has assumed characteristics of the sepal.     

The mutants compacta ?hnlich, Nitida and Grandiflora define developmental compartments and a compensation mechanism in floral development in Antirrhinum majus

In order to improve our understanding of floral size control we characterised three mutants of Antirrhinum majus with different macroscopic floral phenotypes. The recessive mutant compacta ?hnlich has smaller flowers affected mainly in petal lobe expansion, the dominant mutant Grandiflora has overall larger organs, whilst the semidominant mutation Nitida exhibits smaller flowers in a dose-dependent manner. We developed a cell map in order to establish the cellular phenotypes of the mutants. Changes in organ size were both organ- and region-specific. Nitida and compacta ?hnlich affected cell expansion in proximal and distal petal regions, respectively, suggesting differential regulation between petal lobe regions. Although petal size was smaller in compacta ?hnlich than in wild type, conical cells were significantly bigger, suggesting a compensation mechanism involved in petal development. Grandiflora had larger cells in petals and increased cell division in stamens and styles, suggesting a relationship between genes controlling organ size and organ identity. The level of ploidy in petals of Grandiflora and coan was found to be equivalent to wild type petals and leaves, ruling out an excess of growth via endoreduplication. We discuss our results in terms of current models about control of lateral organ size.     

A sensitive flower: mechanical stimulation induces rapid flower closure in Drosera spp. (Droseraceae)

Some plants rapidly close their leaves in response to mechanical stimulation, but no case is known in which mechanical stimulation causes rapid petal closure. In this study, we found that Drosera tokaiensis closes petals within 2–10 min after experimental stimulation of the calyx, closed flowers or scapes with a pair of tweezers. Although petal closure was induced more rapidly by touching a position closer to a flower, it was not induced by stimulating stamens and pistils. The habit of petal closure varies among species of Drosera: after experimental stimulations of the calyx or scapes, D. tokaiensis and D. spatulata often closed petals but D. rotundifolia and D. toyoakensis did not close them. The petal closure may function as defense against a specialist florivore.     

WOOD OF GINKGO IN THE TERTIARY OF WESTERN NORTH AMERICA

Scott , R. A., E. S. Barghoorn , and U. Prakash . (U.S. Geol. Sur., Denver, Colo.) Wood of Ginkgo in the Tertiary of western North America . Amer. Jour. Bot. 49(10): 1095–1101. Illus. 1962. —Woods of Ginkgo and extinct related genera are very rare in the fossil record in contrast to the numerous ginkgoalean leaves. Ginkgo wood may be distinguished from other gymnosperms by a combination of anatomical features herein described. Ginkgo wood from beds of Miocene age at Vantage, Washington, first identified by Beck, is assigned to a new species, G. beckii. Ginkgo wood from the upper Eocene Clarno Formation, John Day Basin, Oregon, is described as G. bonesii sp. nov. Scarcity of fossil ginkgoalean woods may reflect unusual susceptibility to degradation of their cell walls in contrast to the greater chemical resistance to degradation which features many coniferous woods.     

Relationship between petal abscission and programmed cell death in <Emphasis Type="Italic">Prunus yedoensis</Emphasis> and <Emphasis Type="Italic">Delphinium belladonna</Emphasis>

Depending on the species, the end of flower life span is characterized by petal wilting or by abscission of petals that are still fully turgid. Wilting at the end of petal life is due to programmed cell death (PCD). It is not known whether the abscission of turgid petals is preceded by PCD. We studied some parameters that indicate PCD: chromatin condensation, a decrease in nuclear diameter, DNA fragmentation, and DNA content per nucleus, using Prunus yedoensis and Delphinium belladonna which both show abscission of turgid petals at the end of floral life. No DNA degradation, no chromatin condensation, and no change in nuclear volume was observed in P. yedoensis petals, prior to abscission. In abscising D. belladonna petals, in contrast, considerable DNA degradation was found, chromatin was condensed and the nuclear volume considerably reduced. Following abscission, the nuclear area in both species drastically increased, and the chromatin became unevenly distributed. Similar chromatin changes were observed after dehydration (24 h at 60°C) of petals severed at the time of flower opening, and in dehydrated petals of Ipomoea nil and Petunia hybrida, severed at the time of flower opening. In these flowers the petal life span is terminated by wilting rather than abscission. It is concluded that the abscission of turgid petals in D. belladonna was preceded by a number of PCD indicators, whereas no such evidence for PCD was found at the time of P. yedoensis petal abscission. Dehydration of the petal cells, after abscission, was associated with a remarkable nuclear morphology which was also found in younger petals subjected to dehydration. This nuclear morphology has apparently not been described previously, for any organism.     

HIGH-RESOLUTION LEAF X-RADIOGRAPHY IN SYSTEMATICS AND PALEOBOTANY

The foliar vein nets of many seed plants and ferns display systematically informative characters. These venation characters traditionally have been observed by chemically clearing and staining leaves, a process that is slow, involves toxic chemicals, and yields delicate, glass-mounted specimens that require long-term maintenance to prevent or correct bubbling or crystallization of the mounting medium. A technique that uses X-rays and photographic film to produce images of leaf venation consistently shows veins that are 50–100 μm thick. Although the X-ray images are slightly less detailed than the best cleared and stained leaves, the images can be made much more quickly, are more easily stored and reproduced, and do not require permanent alteration of the original herbarium specimen. The technique should facilitate the use of vein characters in systematics, and the identification and systematic analysis of fossil leaves.     

A new species of <Emphasis Type="Italic">Paloue</Emphasis> (Leguminosae: Caesalpinioideae: Detarieae) from Guyana,South America

Paloue sandwithii is described and illustrated from Kaieteur region, Guyana, South America. Characters that distinguish it from the other species of Paloue are the presence of five subequal petals and large coriaceous leaves with prominent venation on the underside of the lamina.     

The diversity of elaborate petals in Isopyreae (Ranunculaceae): a special focus on nectary structure

Elaborate petals are highly diverse in morphology, structure, and epidermal differentiation and play a key role in attracting pollinators. There have been few studies on the elaborate structure of petals in the tribe Isopyreae (Ranunculaceae). Seven genera in Isopyreae (Aquilegia, Semiaquilegia, Urophysa, Isopyrum, Paraquilegia, Dichocarpum, and Leptopyrum) have petals that vary in morphology, and two genera (Enemion and Thalictrum) have no petals. The petals of nine species belonged to 7 genera in the tribe were studied to reveal their nectary structure, epidermal micromorphology and ancestral traits. The petal nectaries of Isopyreae examined in this study were located at the tip of spurs (Aquilegia yabeana and A. rockii), or the bottom of shallow sacs (Semiaquilegia adoxoides, Urophysa henryi, Isopyrum manshuricum, and Paraquilegia microphylla), a cup-shaped structure (Dichocarpum fargesii) and a bilabiate structure (Leptopyrum fumarioides). The petal nectary of eight species in Isopyreae (except A. ecalcarata) was composed of secretory epidermis, nectary parenchyma, and vascular tissues, and some sieve tubes reached the secretory parenchyma cells. Among the eight species with nectaries examined in the present study, A. yabeana had the most developed nectaries, with 10–15 layers of secretory parenchyma cells. The epidermal cells of mature petals of the nine species were divided into 11 types. Among these 11 types, there were two types of secretory cells and two types of trichomes. Aquilegia yabeana and A. rockii had the highest number of cell types (eight types), and I. manshuricum and L. fumarioides had the lowest number of cell types (three types). Aquilegia ecalcarata had no secretory cells, and the papillose conical polygonal secretory cells of D. fargesii were different from those of the other seven species with nectaries. Trichomes were found only in Aquilegia, Semiaquilegia, Urophysa, and Paraquilegia. The ancestral mode of nectar presentation in Isopyreae was petals with hidden nectar (70.58%). The different modes of nectar presentation in petals may reflect adaptations to different pollinators in Isopyreae.

     

Temperature-dependent stomatal movement in tulip petals controls water transpiration during flower opening and closing

Temperature‐dependent tulip petal opening and closing movement was previously suggested to be regulated by reversible phosphorylation of a plasma membrane aquaporin ( Azad et al., 2004a ). Stomatal apertures of petals were investigated during petal opening at 20°C and closing at 5°C. In completely open petals, the proportion of open stomata in outer and inner surfaces of the same petal was 27 ± 6% and 65 ± 3%, respectively. During the course of petal closing, stomatal apertures in both surfaces reversed, and in completely closed petals, the proportion of open stomata in outer and inner surfaces of the same petal was 74 ± 3% and 29 ± 6%, respectively, indicating an inverse relationship between stomatal aperture in outer and inner surfaces of the petal during petal opening and closing. Both petal opening and stomatal closure in the outer surface of the petal was inhibited by a Ca²⁺ channel blocker and a Ca²⁺ chelator, whereas the inner surface stomata remained unaffected. On the other hand, sodium nitroprusside, a nitric oxide donor, had no effect on stomatal aperture of the outer surface but influenced the inner surface stomatal aperture during petal opening and closing, suggesting different signalling pathways for regulation of temperature‐dependent stomatal changes in the two surfaces of tulip petals. Stomata were found to be differentially distributed in the bottom, middle and upper parts of tulip petals. During petal closing, water transpiration was observed by measuring the loss of ³H₂O. Transpiration of ³H₂O by petals was fivefold greater in the first 10 min than that found after 30 min, and the transpiration rate was shown to be associated with stomatal distribution and aperture. Thus, the stomata of outer and inner surfaces of the petal are involved in the accumulation and transpiration of water during petal opening.     

THE MISSING PETAL CHARACTER IN OENOTHERA AND ITS RELATION TO THE CRUCIATE CHARACTER

Two characters are known in Oenothera which show inconstancy of behavior resulting in phenotypic mosaicism. These are absence of petals mp and cruciate petals cr. The latter character has been studied intensively by Oehlkers and Renner. The former is discussed here for the first time. The missing petal character exhibits mosaicism in essentially all cases. Flowers with four, three, two, one, or no petals may appear on the same plant on the same day. Where petals are present, they occupy normal positions and are usually normal in size and shape; where absent, no primordia are produced. It is suggested that the cr character is not based on a highly mutable locus (Oehlkers) or on one in which gene conversion occurs (Renner), but is the result of a mutant gene at a locus basic to the development of sepals which is. capable, under certain conditions, of functioning not only in the sepals, but also in cells of petal primordia, thereby suppressing genes for petal development. The sepaloid tissue which it produces in the petal is much more complex than, the petaloid tissue which it suppresses. The mp locus is basic to the initiation of petals; mp is a mutant gene with reduced potency. Whether it is able to function depends upon the cellular environment in which it finds itself. In both cases mosaicism is the result, not of frequently recurring alteration in genic structure, but of regulation of gene action based on variations in the cellular milieu.     

Homeosis in floral development of Sanguinaria canadensis and S. canadensis ‘Multiplex’ (Papaveraceae)

Sanguinaria canadensis is a member of the Papaveraceae that normally has eight petals rather than four as is usual in the family. Using epi-illumination microscopy to study floral development, we show that the four additional petal primordia are initiated in positions that correspond to the first four stamen positions in species of the Papaveraceae with four petals. Also, these additional petal primordia share early developmental features with stamen primordia: at inception they are circular in outline, and the relationship between organ length and width while very young is similar. The developmental pathway of the additional petals combines both stamen and petal features: initially stamenlike in appearance, they develop into typical petals. The additional petals of S. canadensis can therefore be interpreted as homeotic because petal features are expressed in stamen positions. Organogenesis in the ‘Multiplex’ cultivar is similar to that of its wild progenitor, but during development all primordia in the androecial region become petals. This cultivar, as well as variants within natural populations, show that replacement of stamens with petals occurs within the species.     

Evolution of petal epidermal micromorphology in Leguminosae and its use as a marker of petal identity

Background and Aims

The legume flower is highly variable in symmetry and differentiation of petal types. Most papilionoid flowers are zygomorphic with three types of petals: one dorsal, two lateral and two ventral petals. Mimosoids have radial flowers with reduced petals while caesalpinioids display a range from strongly zygomorphic to nearly radial symmetry. The aims are to characterize the petal micromorphology relative to flower morphology and evolution within the family and assess its use as a marker of petal identity (whether dorsal, lateral or ventral) as determined by the expression of developmental genes.

Methods

Petals were analysed using the scanning electron microscope and light microscope. A total of 175 species were studied representing 26 tribes and 89 genera in all three subfamilies of the Leguminosae.

Key Results

The papilionoids have the highest degree of variation of epidermal types along the dorsiventral axis within the flower. In Loteae and genistoids, in particular, it is common for each petal type to have a different major epidermal micromorphology. Papillose conical cells are mainly found on dorsal and lateral petals. Tabular rugose cells are mainly found on lateral petals and tabular flat cells are found only in ventral petals. Caesalpinioids lack strong micromorphological variation along this axis and usually have only a single major epidermal type within a flower, although the type maybe either tabular rugose cells, papillose conical cells or papillose knobby rugose cells, depending on the species.

Conclusions

Strong micromorphological variation between different petals in the flower is exclusive to the subfamily Papilionoideae. Both major and minor epidermal types can be used as micromorphological markers of petal identity, at least in papilionoids, and they are important characters of flower evolution in the whole family. The molecular developmental pathway between specific epidermal micromorphology and the expression of petal identity genes has yet to be established.Key words: Epidermis, Fabaceae, Papilionoideae, Caesalpinioideae, Mimosoideae, petal surface, scanning electron microscopy, papillose conical cells, tabular rugose cells, tabular flat cells, organ identity     

Determination and Differentiation of Leaf and Petal Primordia in Impatiens balsamina

The development of primordia as leaves, petals, or as organsintermediate between leaves and petals can be regulated by photoperiodin Impatiens. In intermediate organs only some parts of theorgan differentiated as petal, and then only in some cell layers.Allometric measurements of primordium shape suggested that intermediateorgans may begin development as petals, and that their intermediatecharacter at maturity resulted from a switch of some parts ofthe organs from petal to leaf development when the primordiawere between 0.5 and 1 mm long. In reverted apices made to re-flower,primordia were not completely determined as leaves until theywere about 750 µm long. Determination typically occurredfirst at the tips and last at the bases of these primordia.The determination of primordia as leaves or petals in Impatiensis discussed in relation to primordium determination in otherspecies. It is suggested that the lack of commitment to flowermay result in relatively late primordium determination in Impatiens. Impatiens balsamina, determination, differentiation, leaf and petal development, flowering, reversion     

Sink Effect of Cytokinin in Detached Leaves Is Not Caused by Structural Rearrangements of Phloem

The sink effect of cytokinin is manifested as a decrease in source capacity and the induction of sink activity in the phytohormone-treated region of a mature excised leaf. In order to find out whether this effect was due to the direct action of cytokinin on the phloem structure, two types of phloem terminals were examined. In pumpkin (Cucurbita pepo L.) leaves, the phloem terminals are open; i.e., they are linked to mesophyll by numerous symplastic connections, which are located in narrow areas called plasmodesmal pit fields. In broad bean (Vicia faba L.) leaves, the phloem terminals belong to the closed type and have no symplastic links with mesophyll. The electron microscopic study of terminal phloem did not reveal any structural changes in the companion cells, which could account for the suppression of assimilate export. The treatment of leaves with cytokinin neither disturbed the structure of plasmodesmal pit fields in pumpkin leaves nor eliminated the wall protuberances (the ingrowths promoting phloem loading) in bean leaves. No evidence was obtained that the cytokinin-induced import of assimilates in mature leaves is caused by the recovery of meristematic activity, i.e., by either formation of new phloem terminals having immature sieve elements capable of unloading or by the development of new sieve elements within the existing veins. Cytokinin did not induce de novo formation of phloem elements. Structural characteristics of the leaf phloem, such as the number of branching orders in the venation pattern, the number of vein endings per areole, the number of areoles per leaf, the area of one areole, and the number of sieve elements per bundle remained unaltered. It is concluded that the sink effect of cytokinin in excised leaves cannot be determined by alteration of the phloem structure.