. The cell in development and inheritance. Cells. DETAILS OF MITOSIS 83. of centres (without centrosomes), and thus give rise to an irregular multipolar figure (Figs. 36, 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 " ty
. The cell in development and inheritance. Cells. DETAILS OF MITOSIS 83. of centres (without centrosomes), and thus give rise to an irregular multipolar figure (Figs. 36, 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 { sections of root- tips of Alliniu, Lilinui, 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
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectcells, bookyear1906
