No. 450.] STUDIES ON THE TLA NT CELL. 



437 



nuclear spindles) are of two main types: (1 ) thos* 

 with centrosomes, centrospheres or kinoplasmic ca 

 those composed of independent tihrilla- dcvcl(ii)e(l 

 around the nucleus. The latter condition is cspcciall 

 istic of the spore mother cell and is ])crhai)s the hi-li 

 spindle formation known for either animals or plants, 

 interesting to trace the relations of this hii;hcst (. nni 

 lower types through certain lines of evolution to W ( 

 Section VI. 



Spindles with centrosomcs arc known in Sphaccl 

 caulon (Swingle, '97), Dictyota, l-'ig. 4 (Motticr. :( 

 sporangium of Hydrodictyon (Timbcrlakc. .oi), 

 diatoms (Lauterborn, principal paper '96, Kaisicn. ; 

 the basidium (Wager, '94 and Maire, :02). Tlu- b. 

 of the behavior of the centrosomes are gi\cn by 

 Mottier. Indeed there is much doubt about the 

 significance of the bodies in the othc 



their presence at the poles of the 



that they are really centrosomes. The conditions in the diato 

 are especially complicated; an account of Lauterborn s work I 

 been published in English by Rowley, :o3. In Stypocaul 

 Sphacelaria (Fig. 3 c, Section I) and Dictyota (Fig. 4 iHe c. 

 studied have permanent asters which lie at the side of 

 nucleus and which divide just previous to the mitosis and s 

 arate so that they come to lie on opposite sides of the nuck 

 Fibers develop from the centrosomes on the sides nearest 

 nucleus and elongating push against the nuclear membrane i 

 finally enter the nuclear cavity to form the spindle. 



Spindles with centrospheres are well known in Fucus ( I-arr 

 and Williams, '96, '98, Strasburger, •97a), Corallina, Fig. 

 (Davis, '98), in the ascus, Fig. 5 (Harper, '97 and '99), anc 

 the germinating spore of Pellia, Fig. 4 c ( l^armer and Ree^ 

 '94, Davis, :or, Chamberlain, :03). Centrospheres have b 

 reported in other forms but the types mentioned above h 

 received the most careful study. It is probable that the cen 

 sphere is but a larger, more generalized kinoplasmic center t 

 the centrosome, a protoplasmic region whose dynamic activi 

 do not focus so sharply as in the latter structure. There 



