281 



Manif estations of polarity in plant cells which 

 apparently are without centrosomes. 



By 

 W. Marquette. 



With plate XIII. 



The existiiig evidence seems to favor the view that the for- 

 mation of the karyokinetic spindle occurs in quite a different 

 fashion in the animals than in the higher plants. The most fre- 

 quently noted and discussed clifference in the two cases is the 

 presence of the so-called centrosome in the one and its at least 

 apparent absence in the other. While the existence of the centro- 

 some as a permanent cell organ in the animal cell is by no means 

 imiversally admitted, the evidence for its occurrence as such in 

 some cases at least seems unquestionable. The presence of the 

 center, as Rabl and Flemming most clearly pointed out, involves 

 a visible polar Organization in the cell; even in the resting stages 

 the cell shows a polar Organization whose main axis is a straight 

 line passing through the center and the nucleus. When the cell 

 prepares to divide, the centrosome divides first, the two halves 

 separate, and the spindle figure develops about them as centers; 

 from the beginning it is a bipolar figure. At any moment then 

 such cells present a polar, never an isotropic structure. The most 

 thoroughly studied animal cells in general show such an Organi- 

 zation as do also many of the lower plants. Amongst the Algae 

 for example Fucus 1 ) and Dictyota 2 ) show at least during the pro- 

 cesses of division distinct central bodies, and in the apical cells 

 of Stypocaulon 5 ) centre is also present in the resting stages. 



') Sträsburger. E.: Kernteilung und Befruchtung bei Fucus. (Jahrb. 

 f. wiss. Bot. Bd. XXX. 1897. p. 351.) 



2 ) Mottier. D. M. : Das Centrosom bei Dictyota. (Ber. d. Deut. bot. 

 Oesel. Bd. XVI. 1898. p. 123.) Xuclear and cell division in Dictyota dichotoma. 

 (Ann. Bot. Vol. XIV. 1900. p. 163.) 



3 ) Swingle, W. T.: Zur Kenntnis der Kern- und Zellteilung hei den 

 Sphacelariaceen. (Jahrb. f. wiss. Bot. Bd. XXX. 1897. p. 297.) 



