Polymorphic microsatellite markers in the painted dragon lizard,Ctenophorus pictus

We isolated eight polymorphic microsatellite markers from the painted dragon, Ctenophorus pictus, from a genomic library simultaneously enriched for a suite of di‐, tri‐ and tetranucleotide repeat units. Genetic variation was assessed in 40 individuals from populations in Victoria and South Australia. The number of alleles per locus ranged from four to 45 with observed heterozygosity ranging from 0.23 to 0.95. These markers will be useful for studies of natural and sexual selection and the effects of habitat fragmentation in semiarid Australia.     

Early vascular land plants: proof and conjecture

Megafossil evidence does not fill the 'evolutionary gap' between land plants and their hypothetical green algal ancestors. Rare Late Silurian vascular plant megafossils provide little information about the morphological, physiological, biochemical, and ecological steps that preceded their evolution. Dissociated trilete spores, spore tetrads, cuticle- and tracheid-like structures far exceed the abundance and diversity of Silurian vascular plant megafossils, and appear millions of years before them. In reference to whole-bodied organisms, these or analogous structures belong to land plants or emergent aquatics; they may represent plants evolutionarily intermediate between green algae and descendent vascular plants at the bryophyte or pre-bryophyte stages. Changes in the cellular biochemistry of pre-Devonian land plants in response to the selective pressures of terrestrial life may have led to the origin of lignin and cutin, neither of which has any counterpart among the algae, and to the evolutionary surge of the vascular plants in the Early Devonian represented by the plant megafossil record. Positive correlation between abundance and diversity of trilete spores and shallow-water, nearshore sites reinforces conclusions based on morphology that a terrestrial flora existed well prior to the appearance of vascular plant megafossils.     

The Effect of Nitrogenous Fertilizer on the Photosynthesis and Growth of White Clover/Perennial Ryegrass Swards

The application of nitrogenous fertilizer in March to a whiteclover (cv. Blanca) and perennial ryegrass (cv. S23) sward resultedin a rapid suppression of the clover, relative to clover ina treatment given no added nitrogen. Thereafter, the cloverin both treatments grew more rapidly than the grass and itsproportion of the total leaf area in the mixture increased,as the leaf area index rose to 8. After a second applicationof N in early July, clover was not suppressed to the same extentas in the first growth period. Overall, the photosynthetic capacities of newly expanded cloverlaminae were similar in the two treatments. Clover laminae hadhigher photosynthetic capacities than grass, even in the grass-dominant+ N treatment. Lamina area, petiole length, and the number of live leaves perstolon were similar in the two treatments, indicating that thedifferences in total leaf area were due to the presence of fewerstolon growing points in the + N treatment. Trifolium repens L., white clover, Lolium perenne L., perennial ryegrass, nitrogen, leaf area index, photosynthesis, growth     

Relationships between Motor Cell Ultrastructure and Leaf Movements in Samanea saman

We examined the fine structure of motor cells in the secondary pulvinus of Samanea saman (Jacq.) Merrill, to aid in analyzing the cellular basis for K⁺ and Cl^? driven, turgor regulated circadian leaflet movements. Pulvini that were (a) open (horizontal) in the light, (b) closed (vertical) in the dark, or (c) at an intermediate angle after 96-h incubation in H₂O in darkness, were cut into cross sections, sub-divided into quadrants, and prepared for electron microscopy by standard methods. The walls of many cells are ridged, appearing scalloped in cross section, the plasmalemma following the wall contours. Plasmodesmata localized in pit fields are most numerous in the inner cortex of the extensor (abaxial), and least numerous in the outer cortex of the flexor (adaxial) (3.9 and 0.7, respectively, per μm² wall area). Vacuole size, number of vacuoles per cell, and the condition of the electron dense precipitate within the vacuole also vary with cell location, multivacuolation being most pronounced in the outer cortex of the extensor. Chloroplasts are dimorphic: those in cells close to the vascular tissue are very large, circular in cross section, and contain huge starch deposits at all times, while those in the remainder of the cortex are smaller, usually oblong, and contain large starch deposits at the beginning of the dark period, but are devoid of starch at the beginning of the light period. However, both types of chloroplasts in excised pulvini incubated in H²O in darkness for 96 h still contain starch deposits, indicating that (1) light may promote starch degradation, or (2) starch degradation and resynthesis may be rhythmic.     

H. N. Martin and W. K. Brooks: Exemplars for American Biology?

The Johns Hopkins University offered the first modern, American,research-oriented programin biology when it opened in 1876.The program included both physiological and morphological work,so that students could choose either for their advanced degrees.Physiologists studied with Henry Newell Martin, morphologistswith William Keith Brooks. Yet students took courses in bothareas, and the unique exposure to two lines of research andto two very different sorts of teachers made the Johns Hopkinsprogram exceptional. This paper outlines the dual characterof biology at Hopkins, and the particular contributions of bothMartin and Brooks. It also argues that the impact of that uniquedual offering on four of the more famous students, E. B. Wilson,T. H. Morgan, E. G. Conklin, and R. G. Harrison, strongly influencedthe successful and progressive program of research that eachchose.