ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 325 



BOTANY. 



GENERAL, 



Including the Anatomy and Physiology of Seed Plants. 



Cytology, 

 including 1 Cell-Contents. 



Structure of the Cell of the Cyanophycese. — Papers on this hotly- 

 -contested subject still continue to appear. F. Gr. Kohl* gives a general 

 summary of his 'large work on this subject, which appeared a short time 

 ago, and replies to certain criticisms of Brandt. The work of E. W. 

 '01ive,t however, is of the most importance, for by the use of modern 

 methods of fixation, staining, and section-cutting, he claims to have 

 clearly established the existence of mitotic nuclear division in this group. 

 The central nucleus appears to be in a state of continuous mitotic 

 division ; only in the spores and heterocysts do the nuclei enter the 

 condition of rest and exhibit a nuclear vacuole and membrane. The 

 ■ordinary nucleus shows a distinction into a more or less dense or 

 chromatic portion, which encloses a number of minute chromatin 

 granules, the chromosomes, which are of constant number in a given 

 species — 8 in Nostoc commune, for example, and 16 in Oscillatoria tenuis. 

 During actual division there is a definite spindle, and the chromosomes 

 undergo fission, the whole spireme thread, which consists of the chromo 

 somes in a row, undergoing a longitudinal fission. The cell divides by 

 the growing-in of a ring-shaped wall. 



0. P. Phillips % has made a comparative study of the cytology and 

 movements of the Cyanophyceae. He regards the central body in the 

 cell as a nucleus, and describes sexual fusions in the formation of the 

 spores. He finds that the chromatin of the central body is aggregated 

 in hollow vesicles in the resting cell. This vesicular appearance dis- 

 appears in the dividing cell, and the chromatin granules become 

 arranged in a loose network, and multiply by transverse division. 

 ^Nuclear division follows, in one of two ways, both occurring in the same 

 species. One method corresponds to a direct division ; the other is a 

 primitive form of karyokinesis, and resembles the method of mitosis 

 •described by Kohl, in which a double transverse division occurs in the 

 spirem thread, never a longitudinal splitting. The author also found 

 thick-walled spores in Oscillatoria, produced after the fusion of several 

 •cells, and after adjoining " nurse-cells " have disintegrated and given up 

 their chromatin to the spore-cell. This fusion is regarded as a sexual act. 

 He also states that the movements of the Cyanophyceas are caused by 

 •delicate cilia distributed along the sides of the filament. 



* Beih. Bot, Centralbl., xviii. (1904) pp. 1-8. 

 t Tom. cit., pp. 9-44 (1 pi.). 



X Contr. Bot. Lab. Univ. Pennsylvania, ii. (1904) pp. 237-335 (3 pis.). See also 

 Bot. Gazette, xxxix. (1905) pp. 228-9. 



