No. 4S4.] 



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 fibrillffi, which, 

 extending radially into the surrounding cytoplasm (Fig. I'^d), 

 were later (Fig. 1 3 b) 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, Eguisetittn limosui^. rt, prophase of 

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

 older than a\ 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^ B,f,g, Osmunda regalis. d, very early prophase of the first mito- 

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

 ef, prophase, somewhat older than d; fibrillar kinoplasm show'ng polarity. /, still older ; 

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

 ia, b, c, after Osterhout, '97; d, e,/,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 fibrillae. There are 

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

 any stage in the process of spindle formation. 



Smith's (: 00) study of Osmunda presents an important con- 

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



