242 BOTANY 



concerned. In the first place there is the hmer face of the cyto- 

 plasmic envelope surrounding the nucleus and secondly the outer 

 surface of the nucleus. Between the two there is apparently a 

 clear solution. Thus the nuclear membrane is partly cytoplasmic 

 and partly nuclear in origin. It may be due to this fact that there 

 has always been a certain conflict of evidence on the matter. 



Chromosomes. The nature of chromosomes in living material 

 has been investigated by Chambers and Sands in the pollen mother- 

 cells of Tradescantia virginica. The chromosomes in this species 

 are particularly conspicuous structures, and therefore very suitable 

 for work of this nature. The spindle area here forms a hyaline 

 jelly-like mass, less solid than the surrounding cytoplasm and 

 distinctly separated from it. In the living state no evidence could 

 be found for the presence of fibres. The chromosomes lie in this 

 jelly-like mass. They were found to be elastic, jelly-like, nodulated 

 cylinders, which possess a cortex differing markedly in refractive 

 index from the central core. They were also found to be very 

 much more resistant to injury than animal chromosomes. 



Meiosis. Chodat has observed the course of meiosis in the living 

 cells of the orchid, Gymnadenia conopsea. In the megasporocyte, 

 which is only surrounded by a single layer of transparent nucellar 

 cells, the nucleus is seen to show a reticulate structure under 

 oblique illumination. Chodat was able to follow the formation 

 of the leptotene and pachytene threads and the production of 

 gemini. At metaphase the eight gemini became arranged on the 

 equator of the hyaline achromatic figure, and their disjunction 

 and passage to the poles was also observed. In general behaviour 

 the process was apparently very similar to that in fixed material. 



THE MICROSCOPY OF THE CELL WALL 



The meristematic cells of plant tissues and parenchymatous 

 cells possess walls composed mainly of cellulose. The apical 

 meristems of shoot and root frequently do not give the ordinary 

 microchemical reactions for cellulose. According to Tupper-Carey 

 and Priestley, who have investigated the apical cells of the 

 radicle and plumule of Vicla faba with microchemical reagents, 

 these cells do not give the tests for cellulose unless they have been 



