The Movement of Organic Nitrogen Compounds in Plants: With two Figures in the Text

The hypothesis that the movement of organic nitrogen, like thatof carbohydrate, is governed by the prevailing concentrationgradients for the mobile compounds in the phloem has been testedby determining the effect on nitrogen distribution when normaltranslocation was interrupted by ringing in Pelargonium spp.and Vicia faba plants. Nitrogen compounds in the plant tissue were fractionated intoprotein, soluble protein, amide, amino-acid, peptide, nitrate,and ammonia nitrogen. The presence of short-chain peptides inthe extracts was confirmed by paper chromatography. Results showed that accumulation above the ringed zone was confinedto the soluble nitrogen fractions and that amino-acids and possiblypeptides were involved in translocation. The direction of movementmay be determined by the prevailing concentration gradientsof these compounds in the phloem tissue.     

The Effect of Number of Shoots on the Quantity and Distribution of Increment in Young Apple-trees: With three Figures in the Text

It is shown that the shoots of a young tree act additively ratherthan competitively, that is, each extra shoot produces a definiteextra increment in total weight, not that a constant incrementis divided among the shoots of the young tree. One-year apple-trees of 3 varieties were rigorously selectedfor size and weight, and in the spring disbudded to 1, 2, 3,or n, the natural number of shoots per plant. The treatmentswere applied in the 1st or 2nd year after planting and the incrementduring the treatment year was determined. Provided not morethan a few secondary shoots were produced on the current shoots,each additional primary shoot produced an increase in weight.In one variety plants with 1 primary shoot produced many secondariesand these plants were heavier than those with 2 primaries. The largest shoot was not greatly affected in size by the presenceof other shoots except in the variety which produced secondaryshoots readily. These were most abundant on plants with 1 primaryshoot, fewer on plants with 2, and almost negligible on plantswith 3 and n shoots. Treatment and varietal effects on the percentage distributionof increment as leaves, new stem, old-stem increment, and root,were small. The percentage of leaves in the 2nd year was abouthalf what it was in the 1st year; the percentage of root wasnearly the same in both years.     

The Growth of Apple Fruitlets, and the Effect of Early Thinning on Fruit Development: With fourteen Figures in the Text

The development of fruitlets of the apple varieties Cox's OrangePippin and Miller's Seedling was investigated with particularreference to rate and duration of cortical cell division andexpansion. The fruitlet weight increases slowly for the first few daysafter pollination, then exponentially at a rapid rate for about3 weeks, and then at a declining rate until harvest. The rate of cell division is very rapid during the exponentialphase of fruitlet growth, and then the rate declines, but divisioncontinues until about 12 weeks after full bloom in Miller'sSeedling and for at least 6 or 7 weeks after pollination inCox's Orange Pippin. The cells expand exponentially until about 7 weeks after pollination,then continue to expand at a diminishing rate until harvest. Heavy pre-blossom thinning increased fruit size and weight,affecting the rate of both cell division and cell expansion;the differences in fruit weight showed by the 4th week and incortical cell number and cell diameter by the 5th week afterfull bloom.     

The Effect of Annual and Bi-annual Pruning on the Seasonal Changes in Xylem Formation in the Grapevine: With five Figures in the Text

Growth-ring development and seasonal changes in starch contentwere examined in annually as well as bi-annually pruned grapevines.Cambium was generally found to be active (in its normal season)from the middle of April to the end of July, with the main periodof activity being May to June. As a result of an additionalpruning in August a second period of cambial activity beganin the middle of September and lasted until the middle of November,with the main activity occurring in October. In the ‘normal’early summer season cambial activity was found to expand fromthe canes in a basipetal direction, whereas in the late summerseason it recommenced simultaneously in the trunks and canes.In vines that had been pruned twice in the preceding year theearly summer xylem increment was smaller than in those whichhad been pruned only once and the total increment of two growth-ringsper year was similar to that of the one growth-ring in the latter,once pruned, plants.     

Observations on Net Assimilation Rates in Arctic Environments: With two Figures in the Text

Examination of the net assimilation rate (E) during the growingseason in arctic regions by a detached-leaf method revealedno differences between species or with soil richness, but showeda reduction of E with exposure to wind–probably resultingfrom cooling–and a tendency for E to fall towards thelater part of the growing season. E generally lay in the range0·5 to o·8 g./dm.²/week. E for detached leaves ignores respiratory losses in other partsof the plant and is not comparable with E for whole plants;failure to appreciate this confused a previous comparison ofE under arctic and temperate environments. E for detached leavesin temperate summer conditions is normally around 1·1to 1·5 g./dm.²/week. Thus E is reduced in arctic environmentsto about half the value in temperate conditions. This reductionis due mainly to the cold climate.     

Studies on the Physiology of Nodule Formation: With two Figures in the Text: A Reappraisal of the Effect of Preplanting

Nutman (Arm. Bot. 21, 321, 1957) found that preplanting agarslopes with Trifolium pratense L. or Medicago sativa L. advancedthe time when second lots of plants of these species grown onthe same slopes initiated nodules, and depressed the total numberof nodules formed. He attributed these effects to root secretionswhich at low concentration hasten initial nodulation but athigher concentrations inhibit nodule formation. Further workhas now shown that initial nodulation is stimulated becausethe preplant removes traces of nitrate from the medium. Theamount of nitrate in the tap water used to prepare the medium(6?5 p.p.m. N) also increases the number of nodules formed onthe control plants, and this effect explains to a considerableextent the depression of nodule numbers by preplanting. Initial nodulation was delayed by small amounts of nitrate andnitrite but not by other forms of combined nitrogen (ammonium,asparagine, and urea). All forms of combined nitrogen testedincreased the number of nodules formed over a period of 8 weekswhen supplied at an initial concentration of 20 p.p.m. N.     

The Viability of Cereal Seed in Relation to Temperature and Moisture: With eight Figures in the Text

Critical examination of previous work on the viability of cerealseeds shows that there is a simple mathematical relationshipbetween temperature, moisture content, and period of viability.There is evidence that this relationship is similar for wheat,barley, and oats. If the moisture content and temperature ofthe seed is known it is possible to predict the expected lifeof the seed; or alternatively, it is possible to predict variouscombinations of storage conditions necessary to achieve a requiredperiod of viability. These results are discussed in relationto current theories concerned with factors which cause lossof viability in seeds.     

Aspects of Morphogenesis in a Dorsiventral Fern, Pteridium aquilinum (L.) Kuhn: With one Plate and ten Figures in the Text

The formation of the horizontal dorsiventral rhizome of Pteridiumaquilinum from the erect radial axis of the young sporelingis described. The shoot apex and the inception of leaves andbuds at the apical meristem have been investigated, and theirinception is shown to be essentially similar in long and shortshoots, later differences being due to differing rates of growthand internodal elongation in the two types of shoot.     

The Structure and Development of Vascular Nodules in Apple Bud-unions: With two Plates and two Figures in the Text

An account is given of the development of new meristematic centres(vascular nodules) initiated in callus tissue formed in applestems as a result of budding. Both amphivasal (xylem peripheral)and amphicribral (phloem peripheral) nodules occurred, and attentionis drawn to the relationship between the type of nodule formedand the tissue in which it originated. The similarity of thesestructures to the meristematic nodules arising in tissue culturesis discussed, and their possible practical significance as anaid in the rooting of cuttings pointed out.     

Occurrence of Endosperm Haustorium in Cannabis sativa L.: With thirteen Figures in the Text

The development and structure of the chalazal endosperm haustoriumin Cannabis sativa are described. The endosperm is nuclear anda haustorium is formed at the chalazal end. The latter remainsfree nuclear throughout. Enucleate vesicles appear in the upperpart of the endosperm but finally they merge with the cytoplasmof the haustorium. As the embryo reaches maturity it occupiesthe whole seed cavity, the haustorium collapses and the endospermpersists only as a thin layer.     

The Stability of the Growth Pattern of Young Apple-trees under Four Levels of Illumination: With four Figures in the Text

As part of a programme on the characterization of the growthpattern of the apple-tree, uniform I-year-old plants carryingtwo new shoots were grown for a season under 100, 78, 41, or24 per cent, natural light. Weights of leaf, new stem, old stem,and root were determined by sampling on 6 occasions. The dryweightincrements over the whole season ranged from 17 to 151 g. ofwhich, in full light, 22 per cent, was leaf and 22 per cent,was root; in deep shade, 32 percent, was leaf and 8 per cent,was root; and under all conditions 56–60 per cent, wasstem. These percentages were the cumulative result of currentrates of growth of leaf, stem, and root over the whole growingperiod. The rates were not constant relative to one another,but the much greater quantity of growth made over the period100–200 days from bud-break swamped earlier differences.All treatments showed the same basic pattern of growth withminor differences increasing with the intensity of shading.These differences are discussed in relation to utilization ofreserves and the demands of the various regions of the plant.The response to shading was analysed into the effects of reducedlight interception, increased leaf dispersion, increased leafproportion, reduced length of growing season, and lighter leafweight at the beginning of the 20-leaf stage. The result ofthese factors was a doubling of the growth expected in the absenceof response. It was concluded that the pattern of growth isstable, and the conditions for the perpetuation of such stablepatterns as a necessary qualification for tree growth are brieflydiscussed.     

Leaf Development in Narcissus pseudonarcissus L.: With twenty Figures in the Text: The Comparative Development of Scale and Foliage Leaves

Details are given of the distribution of cell division and cellelongation in various tissues of the daffodil leaf. The development of the vascular system is also described, andrelated to the intercalary growth of the leaf. The productionof a new longitudinal vascular strand appears to be determinedby the number of cells between the existing strands. The scale and foliage leaves appear to originate from similarprimordia. Their developments diverge when they are about 1mm. long; a scale leaf is developed where most cell divisionsoccur in the sheath, and a foliage leaf is formed where thereis a region of more rapid cell division at the base of the blade.     

The Heterotrophic Nutrition of Chlorella vulgaris (Brannon No. 1 Strain): With two Figures In the Text

A range of sugars, sugar alcohols, sugar phosphates, organicacids, and monohydric alcohols have been tested as carbon sourcesfor growth and as respiratory substrates using Chlorella vulgaris,Brannon I, grown in darkness. Much higher rates of growth and respiration were obtained withd-glucose than with any other substance tested. Ethanol (at0·005 M.) sustained both growth and respiration at c.50 per cent, of the level with glucose (0·028 M. or higher).Evidence was obtained that the organism can become ‘adapted’to utilize d-galactose and sucrose as effective carbon sources.Sustained growth was not obtained with any of the other substancestested. The glucose monophosphates, methanol and certain organic acids(oxalacetate, -ketoglutarate, cis-aconitate, and pyruvate) clearlystimulated oxygen uptake but to a less extent than ethanol.The other substances tested were either inhibitory to respirationor inactive or of very low activity as substrates. The growth in darkness and in liquid culture of Chlorella whensupplied with d-glucose was insensitive to pH over the range4·5 to 7·0 and was markedly enhanced by a highlevel of aeration. Gains in cellular dry weight ranging from45 to 90 per cent, of the weight of d-glucose disappearing fromthe culture medium were recorded in growth experiments; measurementsof CO₂ evolution in the Warburg indicated retention of up totwo-thirds of the glucose-C in cell material.     

Physiological Investigations on the Banana Plant: With seven Figures In the Text: Factors Which Affect the Nitrogen Compounds of the Fruit

A quantitative study has been made of the way in which the nitrogenouscompounds which are present in the banana fruit are affectedby the changes that ensue subsequent to harvest. This was donewith special reference to Musa acuminate cv. Gros Michel asgrown in Central America (Part A), but comparative data arefurnished for the cultivars and for material from other areasof cultivation (Part B). In the cultivar Gros Michel from Honduras,the amides (asparagine and glutamine) and histidine play a predominantrole in the soluble nitrogen fraction of the fruit. Prominentchanges occur in the nitrogen (N) compounds as the fruit ripens,and these are shown to be markedly influenced by the conditionsthat obtain during the development of the fruit. The nitrogenouscomposition of the fruit (Gros Michel) is markedly affectedby the season of the year at which it forms (Part C); this affectsthe balance between the amides (asparagines and glutamine) andhistidine, and also influences the post-harvest metabolic behaviourin ways which are described. While the total protein of thefruit is relatively stable in its amino-acid composition, certaindifferences are noted which seem to characterize the cv. GrosMichel as it grows in Central America, and some shifts in theamino-acid balance in the protein do seem to occur with ripening. A typical growth curve for the parthenocarpic fruit of M. acuminatecv. Gros Michel is given, and the changes in the N compoundsthat occur during development (Part D) are related to this andto the seasonal effects referred to in Part C. The very young inflorescence is first relatively rich in solubleN compounds. After the early phase of growth (cell division)has elapsed, the fruit utilizes its soluble N in synthesis fasterthan it is supplied to the fruit, so the soluble N complementfalls to a low level; thereafter it increases again to a newhigher level at harvest. The composition of the soluble N fractionas stored at harvest is quite different from that which obtainsin the inflorescence in which the fruit is being initiated.The latter emphasizes the amides (asparagine and glutamine)and hi8tidine; the former emphasizes alanine and glutamine asthe only prominent amide. The trend of events is markedly affected by the time of yearwhen the fruit develops—development in the winter leadingto a low amide (especially glutamine)/ high histidine condition;whereas development in the summer leads to a high amide (asparagineand glutamine) /low histidine condition at the normal time ofharvest. In the more rapid development of summer-grown fruit,certain changes in N compounds occur after harvest, which inthe slower developing winter-grown fruit precede the harvest. The different regions of the fleshy fruit, i.e. the fleshy pericarp(endocarp) and the inner region composed of carpels, differgreatly in the total quantity and in the composition of thenitrogenous compounds they contain. The carpels are richer insoluble N and contain all of the amide of the ripe fruit.     

Studies in the Physiology of Lichens: With two Figures in the Text: The Effects of Starvation and of Ammonia Absorption upon the Nitrogen Content of Peltigera polydactyla

Discs cut from the thallus of the lichen Peltigera polydactylacontain relatively large amounts of ammonia nitrogen and smallamounts of amide nitrogen. During starvation in the dark theamounts of ammonia and amide nitrogen remain unchanged, butthe amount of amino-nitrogen increases. Absorption of ammoniaresults in increases in the amounts of ammonia and amino-nitrogenin the discs, but not in the amount of amide nitrogen. It istherefore concluded that amides do not have an important quantitativerole in the nitrogen metabolism of the discs. Ammonia absorption is stimulated by addition of glucose to themedium, but the very slow rate of protein synthesis is onlyslightly increased by glucose. The rate of nitrate absorptionis much slower than that of ammonia absorption. The ecological implications of the results are discussed, andexisting knowledge of the nitrogen metabolism of lichens isreviewed.     

Wind and Water Dispersal of Wetland Plants Across Fragmented Landscapes

Biodiversity in wetlands is threatened by habitat loss and fragmentation, of which agricultural activities often are a cause. Dispersal of plant seeds via wind and ditches (water) may contribute to connecting remnant wetland plant populations in modern agricultural landscapes, and help to maintain and restore biodiversity. We developed a spatially explicit model to assess the relative importance of dispersal by wind and dispersal by water through drainage ditches for two wetland plant species in agricultural landscapes: a typical wind disperser and a typical water-disperser. Simulation results show that the typical wind disperser had a much higher capability to disperse by wind (90th percentile <30 m) than the typical water-disperser (90th percentile <2 m). Surprisingly, the capability to disperse via water was similar for the two species: 90th percentile dispersal distances following a combination of wind and water dispersal were between approximately 100 and 1000 m. Dispersal by water transported more seeds over long distances for both species. The main determinants for dispersal distance by water were roughness of the ditch (determined by, for example, bank vegetation) and the presence of obstructions (for example, culverts). Density or direction of the ditch network did not seem to affect water dispersal distances substantially. From a biodiversity conservation perspective, it would be most useful if areas with suitable riparian wetland habitat were intersected with a network of shallow ditches with a high roughness promoting seed deposition. These areas should then be connected to other suitable areas by a few regularly cleaned ditches with no obstructions and low seed trapping probability.     

Life History and Reproduction of Furcellaria fastigiata (L.) Lam: With two Plates and two Figures in the Text: The Tetrasporophyte and Reduction Division in the Tetrasporangium

The tetrasporophyte of Furcellaria fastigiata (L.) Lam. is diploidand has 68 chromosomes. The plant is morphologically similarto, though slightly greater in stature than, the gametophyticplants, both of which have 34 chromosomes. Tetrasporangial initialsappear in May and reduction division takes place in early November.The process of meiosis is basically very similar to that ofhigher plants. A modified iron alum aceto-carmine staining schedulegives satisfactory staining of the chromosomes of this plant.     

On the Seed Vesquia tournaisii C. E. Bertrand, from the Belgian Wealden: With two Figures in the Text

This hitherto little-known seed is redescribed from two newspecimens. The structure of the stone and internal cutinizedmembranes is described. The new knowledge tends to confirm theattribution of this seed to the Taxopsida.     

The Effect of Root Temperatures on Water and Sulphate Absorption in Intact Sunflower Plants

The effect of 15, 25, and 35°C root temperature on waterabsorption, transpiration, and sulphate uptake by the rootsand transport to the shoots of intact sunflower plants has beenstudied using 0.5, 5.0, and 50.0 mM sulphate concentrationsat two rates of transpiration induced (1) by light and low relativehumidity and (2) by darkness and high relative humidity. Root temperatures and sulphate concentrations did not significantlyaffect the water absorption and transpiration and both theseprocesses were approximately similar at the different treatments.There was a nearly twofold increase in water absorption andtranspiration in the light and low relative humidity as comparedto the dark and high relative humidity irrespective of the roottemperatures and sulphate concentrations. The A.F.S. uptake in the roots was found to be independent ofthe root temperatures, sulphate concentrations, and transpirationrates, and amounted to 15 to 21 per cent based on the root weight.Sulphate accumulation in the roots was not significantly influencedby the root temperatures at 0.5 and 5.0 mM sulphate concentrations,but nearly doubled with temperature at 50.0 mM sulphate concentrationof the external solution. The slow nature of accumulation ofsulphate, the high sulphate status of the experimental plants,and the short duration of the experiments are considered aslikely reasons for the absence of a clear effect of temperatureson accumulation of sulphate at the two lower concentrationsof the external solution. Effects of high concentration on permeabilityand metabolism of the cells are suggested as the reasons forthe decreased accumulation with an increase in temperature at50.0 mM sulphate concentration. Accumulation of sulphate inthe roots was not significantly influenced by the transpirationrates. Unlike root accumulation, sulphate transport to the shoots increasedwith increasing transpiration. However, a major part of thesulphate transport (70 to 75 per cent at 0.5 and 5.0 mM sulphateconcentrations and 80 to 85 per cent at 50.0 mM sulphate concentration)appeared to have occurred at the low transpiration. The similarityof this transport to the accumulation of sulphate in the rootsindicates that it was due to an active transport process sensitiveto root temperatures and sulphate concentrations. A low concentrationof sulphate in the xylem and an increased permeability of theroot cells to ion movement induced by an increased suction inthe xylem are considered as reasons for a small increase inthe sulphate transport at high transpiration rate. The evidencefor the existence of a barrier—probably endodermis—preventingthe passive diffusion of sulphate and sensitivity of the TranspirationStream Concentration to root temperatures and sulphate concentrationsfavour that the increased transport with increased transpirationwas due to an active process.