82 CELL-DIVISIOX 



spi>iul in funclion to those of the eentral sinndle and to the mantle- 

 fibres. It seems probable that the difference between the two types 

 of spindle-formation niav be due to, or is correlated with, the fact 

 that the nuclear transformation takes place relatively earlier in the 

 first type. When the nucleus lags behind the spindle-formation the 

 centrosomcs take up their position prematurely, as it were, the cen- 

 tral spindle disappearing to make way for the nucleus. 



It is m the mitosis of plant-cells that the most remarkable type of 

 achromatic figure has been observed. In some of the lower forms 

 (Algae) mitosis has been clearly shown to conform nearly to the 

 process observed in animal cells, the amphiaster being provided with 

 verv large asters and distinct centrosomes, and its genesis corre- 

 sponding broadly with the second type described above (Figs. 32, 33), 

 though with some interesting modifications of detail.^ Swingle ('97) 

 describes in Stytopocaiilon a process closely similar to that seen in 

 many animal cells, the minute but very distinct centrosomes being 

 surrounded by quite typical cytoplasmic asters, passing to opposite 

 poles of the nucleus, and a spindle then developing between them 

 out of the achromatic nuclear substance (Fig. 32). In the flowering 

 plants and pteridophytes, on the other hand, mitosis seems to be of a 

 quite different type, apparently taking place /;/ tJie entire absence of 

 centrosomes. Guignard ('91, i, '92, 2) clearly described and figured 

 typical centrosomes and attraction-spheres both in the ordinary 

 mitosis (Fig. 34) and in the fertilization of the higher plants, giving 

 an account of their behaviour nearly agreeing with the views then 

 prevailing among zoologists. Although these accounts have been 

 supported by some other workers,^ and have recently been in part 

 reiterated by Guignard himself ('98, i ), they have not been sustained 

 by some of the best and most careful later observers, who describe a 

 mode of spindle-formation differing radically from that seen in thal- 

 lophytes and in animals generally.^ According to these observations, 

 begun by Farmer and Belajeff, and strongly sustained by the care- 

 ful studies of Osterhout, Mottier, Nemec, and others, the achromatic 

 figure is almost wholly of cytoplasmic origin, arising from a fibrillar 

 material (" kinoplasm " or " filar plasm," of Strasburger), which at the 

 beginning of mitosis forms a net-like mass surrounding the nucleus, 

 from which fibrillae radiate out into the cytoplasm. As the nuclear 

 membrane fades, these fibrillae, continually increasing, invade the 

 nuclear area, gather themselves into bundles, converging to a number 



1 See especially Swingle ('97) on Sp/iacelariacecr, Strasburger ('97) on Fucits, Mottier 

 ('98) on Dictyota ; cf. also Harper ('97) on Erysiphe and Peziza. 



2 Cf. Schaffner ('98), Fulmer ('98). 



3 See Osterhout ('97) on Equisetum,Vi.o\.'i\^x ('97, i, '97,2) on Lilium, Lawson ('98) on 

 CobcEci, Nemec ('99) on Allium, Debski ('97, '99) on Chara ; also Belajeff ('94) and 

 Farmer ('95). 



