588 SUMMARY OF CURRENT RESEARCHES RELATING TO 



BOTANY. 



GENERAL, 



Including the Anatomy and Physiology of Seed Plants. 



Cytology, 

 including- Cell-Contents. 



Polar Caps in Smilacina.* — H. D. Densmore has investigated the 

 structure and function of the polar caps found in the dividing cells of 

 the root-tips of Smilacina amplexicauUs. The author finds that these 

 cells have a cytoplasm composed of a fibrous network and granules, and 

 that preparatory to nuclear division the cytoplasm is unusually dense at 

 the poles of the nuclei. The caps which develop from this cytoplasm 

 are differentiated into a limiting layer and a lighter central core of 

 meshes. Spindle fibres arise from the cap, and the latter is gradually 

 transformed into a spindle. Multipolar caps resembling those in the 

 pollen-mother-cells are often formed, and form an important link of 

 connection between the diarch spindles of vegetative cells and the multi- 

 polar polyarch spindles of sporogenous cells. Two distinct types of caps 

 and spindles are found in the exodermal layer, viz. ordinary diarch caps 

 and spindles, and monarch caps and spindles. 



Reduction Division in Agave virginica.f — J. H. Schaffner has 

 studied the reduction division in the pollen-grains of Agave virginiea. 

 He finds that the resting nucleus contains chromatin granules which 

 are massed together according to the reduced number of chromosomes ; 

 each mass probably represents a bivalent protochromosome. These 

 masses unite and elongate until a spirem of chromatin granules is formed. 

 The granules undergo transverse division, and the spirem shortens and 

 arranges itself into twelve loops of varying size and shape. These 

 loops form a wreath-like circle, which breaks up into four long, twisted 

 chromosomes, three ring-shaped chromosomes, and five small bean- 

 shaped chromosomes. By means of connecting fibres, the chromosomes 

 are drawn into the equatorial plane. One or two nuclei are present, 

 and persist after spindle-formation ; they are sometimes thrown bodily 

 out of the cytoplasm. The spindle is always bipolar, and the poles 

 are like dome-shaped caps similar to those seen in vegetative karyo- 

 kinesis. Definite asters are to be seen at the poles. The chromosomes 

 divide transversely during metakinesis. The masses of chromatin in 

 the resting daughter-nuclei represent twelve daughter-chromosomes. 

 In the second division the chromosomes divide longitudinally. 



Mitosis in Fucus.J — S. Yamanouchi has studied the life-history of 

 Fucus vesiculosus, with the following results. The nuclei of the vege- 



* Univ. California Publications, Bot., iii. (1908) pp. 303-30 (5 pis.). 

 t Bot. Gaz., xlvii. (1909) pp. 198-214 (3 pis.). 

 % Tom. cit., pp. 173-97 {i pis.). 



