Karyological Anatomy of Fibre Development in the Leaves of Agave americana L. var. marginata alba Trel.

From a study of 100 metaphase plates in root-tip squashes and75 fibre-cells in leaf-base squashes, it is found that the chromosomenumber, although having an irregular type of variation, commonlytend to occur as multiples of 15, the haploid number. In developingfibre-cells the tendency of complete endomitosis (resultingin 2n, 4n, and 8n numbers) is stronger than the partial endomitosis(resulting in 5n, 6n, 7n, etc.). Nuclear volumes of fibre-cellsalso roughly correspond to 2K, 4K, and 8K. Significant linearcorrelations between chromosome number and nuclear volume andbetween nuclear volume and fibre-cell volume has been obtained.Thus the development and differentiation of fibres involve completeand partial endomitoses, accompanied by somatic non-disjunctionphenomena.     

DNA-dependent RNA Polymerase associated with Bacteriophage PM2

A DNA-dependent RNA polymerase is associated with purified preparations of bacteriophage PM2. The template is DNA, as suggested by the reduction in polymerase activity on treatment of disrupted virus particles with DNAase and by the absence of detectable amounts of RNA in the virus.     

Development of Leaf Forms in Ipomoea reptans (Linn.) Poir

Development of leaves of two chromosomal biotypes of Ipomoeareptans, one with broad leaves and the other with narrow leaves,was studied. Early development of the ‘narrow’ typeinvolves a rapid multiplication of cells without expansion.This phase is followed by cell enlargement with a negligibleamount of multiplication. In the ‘broad’ type onthe other hand, multiplication and enlargement are simultaneousand proceed slowly, but steadily. The lamina shape of both thebiotypes is primarily related to a difference of cell multiplicationrate in the basal, median and apical parts. Some gradient influencingcell multiplication probably exists from the base to the tipof lamina, the optimum point being in the middle. Maturationand enlargement of cells is basipetal and continuous. The wavynature of the leaf margin is related to a very accurate geometricaladjustment of cell number variation in depressions and mounds,which may be controlled by a product of the lateral veins.