198 BOTANICAL MICROTECHNIQUE. 



This method has also proven good for following the 

 fate of the crystalloids during karyokinesis (Zimmermann, 

 III, 119). 



2. The Centrospheres. 



348a. After the presence of the so-called centrospheres * 

 or attractive spheres had been recognized in animal cells by 

 various authors (cf. Flemming I and III), Guignard (IV) suc- 

 ceeded in observing them in various plant-cells also, and it 

 is now to be regarded as not improbable that these bodies 

 are constant constituents of the cell. 



The centrospheres, which have also been called by Guig- 

 nard ''spheres directrices" consist of a generally globular 

 central portion (the " centrosome" of Guignard) which is 

 surrounded by an unstainable envelope, and occur usually 

 a pair in each cell (cf. Fig. 35 and 36, a). 

 They appear to play an important part, 

 especially in karyokinesis. At least, 

 they form, after their separation, the 

 centres of the radiating structures ob- 

 served in the cytoplasm (cf. Fig. 36, 

 II) ; and the threads of the achromatic 

 spindle (cf. 342) run together at both 

 FIG. 35. Embryo-sac of Li- ends at the attractive spheres (cf. Fig. 



Hum Martagon before the - TTT JTAT\ At j.t- .*- 



first nuclear division. , 36, III and IV). At the same time 



centrospheres. After Guig- . T,, r . i_ r i.t~ 



nard. with the splitting of the segments of the 



nuclear threads, a division of the centrospheres occurs, so 

 that each daughter-nucleus has again two attractive spheres 

 {cf. Fig. 36, IV), which at first remain together, and separate 

 only at the beginning of another nuclear division. 



In the sexual act of the Angiosperms, according to Gui- 

 gnard's observations, the attractive spheres of the male 

 nucleus enter the egg-cell at the same time with it, and the 

 spheres of male and female origin fuse in pairs (cf. Fig. 37). 



*[This English equivalent of the term lately proposed by Strasburger for 

 these structures seems, on the whole, the most available name for them. 

 The non-staining envelope of the centrosome may be termed, with Stras- 

 burger, the astrosphere.\ 



