No. 454.] 



STUDIES ON THE PLANT CELL. 



733 



Osterhout's ('97) account of spindle formation in Equisetum 

 is noteworthy. He found that the nucleus of the spore mother- 

 cell became surrounded by a web of delicate fibrillse, ^vhich, 

 extending radially into the surrounding cytoplasm (Fig. I3#), 

 were later (Fig. 13^) gathered into numerous pointed bundles 

 or cones. After the dissolution of the nuclear membrane these 



FIG. 13. Spore mother-cells of Pteridophytes. a, 6, c, Equisetum limosum. a, prophase of 

 first mitosis; the radially disposed fibrilla? are gathering together into cones, b, prophase, 

 older than; the nuclear membrane has broken down and the fibrillae have entered the 

 nuclear cavity; the cones lie in two groups opposite one another, c, just before meta- 

 phase ; the fibrillar cones are nearer together and the chromosomes have gathered to form 

 the nuclear plate, d, e,f, g, Osmunda regalis. d, very early prophase of the first mito- 

 sis; nucleus in the spirem stage surrounded by a granular and fibrillar zone of kinoplasm. 

 e, prophase, somewhat older than d\ fibrillar kinoplasm showing polarity, f, still older; 

 chromosomes formed; one pole of spindle developed, g, metaphase; a tri-polar spindle. 

 (a, b, c, after Osterhout, '97; d, e,f,g, Smith, :oo.) 



cones arranged themselves side by side in two sets to form the 

 spindle of metaphase (Fig. 13^). The spindle is then from the 

 outset multipolar, and even though some of the cones unite when 

 they become grouped around a common axis, nevertheless the 

 poles of the spindle at metaphase show their composite nature in 

 the absence of a common focal point for the fibrillas. There are 

 no centrosomes at the poles and no reason for their presence at 

 any stage in the process of spindle formation. 



Smith's (: oo) study of Osmunda presents an important con- 

 firmation of Osterhout's conclusions that the spindle in pterido- 



