DETAILS OF MITOSIS 



83 



r 



of centres (without centrosomes), and thus give rise to an irregular 

 multipolar figure (Figs. 16, 133). This figure finally resolves itself 

 into a definite bipolar spindle which is devoid of centrosomes, and 

 in the earlier stages also of asters, though in the later phases some- 

 what irregular asters are formed. On the basis of these observations 

 Mottier^ proposes to distinguish provisionally two well-defined types 

 of mitosis in plants which he designates as the "thallophyte " and the 

 "cormophyte" types. The latter seems wholly irreconcilable with 

 the process observed in animal-cells ; for the whole course of spindle- 

 formation seems diametrically opposed in the two cases, and should 

 the cormophyte-type be established it would, to say the least, greatly 

 restrict the application of the centrosome-theory of Van Beneden and 

 Boveri. Only future re- 

 search can definitely de- 

 termine the question. 

 There can be no doubt 

 that the descriptions of 

 Guignard and his follow- 

 ers do not rest upon pure 

 imagination ; for it is easy 

 to observe at the spindle- 

 poles in some prepara- 

 tions {e.g. sections of root- 

 tips of A/liuju, Lilinni, 

 etc. ) deeply staining- 

 bodies such as these 

 authors describe. These 

 "centrosomes" seem, 

 however, to be of quite 

 inconstant occurrence ; 

 and the careful studies of 

 Osterhout, Mottier, and Nemec seem to give good ground for the 

 conclusion that they have no such significance as the centrosomes of 

 lower plants or of animals. It should nevertheless be borne in mind 

 that true centrosomes (" blepharoplasts ") have been demonstrated in 

 the spermatogenic divisions of some of the vascular cryptogams, and 

 that analogous bodies occur in the corresponding divisions of the 

 cycads (p. 175). We should therefore still hold open the possibility 

 that centrosomes may occur in the vegetative mitoses of the higher 

 plants, their apparent absence being possibly due to lack of staining- 

 capacity or similar conditions rendering their demonstration difficult.^ 



1 '97, 2, p. 1S3. 



2 Mentio7i may here be made of the barrel-shaped truncated spindles described in some 

 of the plants. In Basidiohohis, Fairchild ('97) finds spindles of this type, having no asters 



D . . 



Fig. 33. — Mitosis in ascus-nuclei of a fungus, Etysiphe. 

 [Harper.] 



A. Resting nucleus with disc-shaped centrosome (c). 

 B. Early prophase with aster. C. Later prophase ; amphi- 

 aster; intranuclear spindle forming. D. Spindle estab- 

 lished. E. Daughter-nucleus after division ; spore-mem- 

 brane developing from astral rays. 



