Variations in the Germination-rate and Development of Fern Spores in Culture

In fern prothalli growing in pure culture, a number of variationshave been observed in the rapidity of the germination of sporesand the subsequent growth of the prothalli. Although these variationshave not all been satisfactorily explained, experiments showthat it is possible to produce considerable changes in the germinationand growth of fern spores by introducing fungal contaminationand prothallial extracts into the media on which they are sown.These changes are considered in relation to variations in thedevelopmental morphology of spores in pure culture and it issuggested that indole-3-acetic acid may be the active substanceinvolved.     

Light measurement and the terminology of low

Abstract. This paper (i) considers the measurement of light in terms of the flow of radiant energy or of particles in a vector field; (ii) derives terminology and units for the specification of light as a flow of radiant energy or of photons which satisfy both the requirements of SI and are physically consistent and (iii) recommends that this terminology is adopted by all plant scientists to avoid ambiguity, confusion and the proliferation of synonyms when reporting light measurements.     

The Effect of Colchicine on Spermatogenesis in a Fern, Pteridium aquilinum (L.) Kuhn

Treatment of developing antheridia of Pteridium aquilinum for24 h with radioactive and normal colchicine resulted in spermatocyteswith restitution nuclei, binucleate spermatocytes with multipleimmature blepharoplasts, and spermatids in which the organizationof the microtubular ribbon and basal bodies, and the shapingof the nucleus were seriously disturbed. The results indicatethat the coiling of the multilayered structure and the condensationof the chromatin, two key events in spermatogenesis, are independentof tubulin polymerization. Transitional stages were observed between the granular materialof the blepharoplast and microtubules. Colchicine affected theassembly of the cartwheel structure of the basal bodies lessthan that of the triplets, which were often rudimentary or absent.Autoradiographs were only partially successful because of thefailure to devise a satisfactory method of embedding by freeze-substitution,but there was clear evidence of colchicine binding by nucleiin young spermatocytes. Pteridium aquilinum (L.) Kuhn, bracken, spermatogenesis, colchicine     

Studies in the Genus Elaphoglossum Schott: I. Stelar Structure in Relation to Habit

The habit is described of a number of species of Elaphoglossumcollected in Jamaica. Species were present with creeping horizontalrhizomes, shortly creeping or ascendent rhizomes, and one specieswith an ascendent or upright rhizome. The stelar structure of these rhizomes is described and it isshown that it bears a relation to the habit of the rhizome. A preliminary examination of the apices has shown that the symmetryof the rhizome is determined in the initiation of the primordialtissues; it is not secondarily induced by the habit of the rhizome. The occurrence of dormant buds is noted in all the species examined.     

The Vascular Pattern of Italian Ryegrass (Lolium multiflorum Lam.) 2. Development of the Seedling Axis to Maturity

The vascular system present in a grass seedling axis persistsin a functional state at the base of a maturing plant, but undergoesa number of modifications. Two strands of phloem, accompanied by some internal xylem, differentiatein association with the bicollateral mesocotyl trace at rightangles to the existing phloem, resulting in a tetrarch bundle.Lateral seminal roots are themselves tetrarch and the vascularinsertion of a seminal root on to the mesocotyl is a distinctivethree-dimensional feature. At the base of the mesocotyl thetetrarch bundle merges with the tetrarch bundle of the primaryseminal root via a transition zone. The four phloem poles uniteand then diverge again; the central xylem strand splits intothree and then reunites, the two tissues being intimately interlockedby this rearrangement. The additional vascular tissue of the mesocotyl extends up intothe coleoptilar node and becomes involved in the vascular attachmentof nodal roots at this point. Additional vascular tissue continuesto differentiate in the periphery of the maturing stem and ishere termed the ‘peripheral plexus’. In the seedling, the xylem of the ‘bridge’ linkingthe mesocotyl trace with the scutellar trace is associated withxylem transfer cells and also contains tracheids with distinctive,thin-barred scalariform thickening. These transfer cells disappearas the plant matures but numerous tracheids with thin-barredscalariform thickening are then to be found. The possible significanceof transfer cells in the coleoptilar node is discussed.     

The effect of rabbit (Oryctolagus cuniculus) grazing damage on the growth and yield of winter cereals

In 1986/1987 and 1987/1988 wild rabbits (Oryctolagus cuniculus) were trapped and enclosed in a 0.3 ha site in which two varieties of winter barley (Igri and Panda) and two of winter wheat (Norman and Mission) were grown in a split plot block design experiment. The level of rabbit population was varied to emulate natural variation in numbers throughout the growing season and was regulated to produce a peak density of 77 rabbits ha^-* in the first year, and 33 rabbits ha^-1! in the second year. Grazing was managed by the use of exclosure fences around plots to produce four treatment levels - protected, autumn grazed, spring grazed and totally grazed regimes. Rabbit damage was assessed using stem and leaf damage indices several times through the growth of the crops. Yields were measured in terms of head number, grain weight and total yield. There was no evidence of varietal preference among the four cereal varieties on the basis of damage assessments. In the first year the totally grazed treatment led to an increase in the number of unripe heads present at harvest which would indicate a delayed harvest date in a field crop. Winter wheat showed a trend towards higher yield loss in spring-damaged plots, possibly linked to the time of tillering in this crop. Yield losses overall were highest in those plots grazed in either the autumn or throughout the entire season. The level of peak rabbit population did not appear to influence the degree of loss in either year. The results indicate that there may be a threshold of rabbit damage early in the growth of the crop which contributes most to the yield loss. This emphasises the importance of protecting a winter cereal crop at its establishment phase.     

Adaptive architecture in rhizomatous plants

The architecture of few rhizomatous plants has been studied in any morphological detail: a great many of those which have been studied show highly organized and repetitive branching patterns. These branching patterns are largely confined to three basic types: those based on a ± 60° branching angle, those based on a ± 45° branching angle, and those with a predominately linear component. These various configurations must confer certain advantages in terms of substrate exploration and exploitation. The consistent architecture of many rhizomatous plants permits predictive graphic simulation of the branching patterns, and also permits estimates to be made of productivity in terms of meristem/shoot accumulation. As a background to this structural consideration of rhizomatous plants, an extensive bibliography is presented in an appendix, covering all aspects ot rhizomatous and stoloniferous growth.