THE CENTROSOME AND THE BLEPHAROPLAST. 45 
continuity of the centrosomes; but from the fact that no such organs 
exist in the higher plants, and that they seem to be wanting in many 
Thallophyta as well, this view is greatly weakened, if not rendered 
quite untenable. 
On the zoological side of the question, the recent researches of Wil- 
son (1901) on eggs of Zoxopenustes, which were made to develop 
parthenogenetically through certain stages by means of chemical 
stimuli, throw new light upon the subject. In segmenting eggs 
induced to develop parthenogenetically by means of a treatment with 
suitable solutions of magnesium chloride, numerous asters (cytasters) 
often made their appearance in the cytoplasm in addition to the nuclear 
asters. Similar asters may arise also in non-nucleated fragments of 
eggs. These ‘‘ cytasters,” just as the segmentation or nuclear asters, 
may consist of a very distinct centrosome upon which is centered a 
system of beautiful radiations. The centrosomes divide, and a central 
spindle is formed between the daughter centrosomes. In fact, the 
‘¢ cytasters ” are exactly like the normal cleavage-asters arising in con- 
nection with the chromatin. As the evidence seems conclusive that 
the ‘‘cytasters” arise de zovo, Wilson concludes that centrosomes 
occurring normally in cells arise also de zovo, and that the doctrine 
of the genetic continuity of the centrosome is untenable. 
It is not known whether anything comparable to these ‘ cytasters” 
ever occurs in a plant egg-cell, which may be made to develop parthe- 
nogenetically by artificial means, and consequently we cannot accept 
the conclusion upon this basis as applicable to plants. There are, 
however, in plants many well established facts which argue strongly 
against the view that the centrosome or centrosphere is an organ of 
morphological rank. 
In 1897, the author made the unqualified statement, to which he 
still adheres, that centrosomes or centrospheres do not occur in the 
higher plants, and nearly all research since made along this line has 
only confirmed this view. We know now that the structures which 
Guignard so beautifully figured in 1891 for cells of Zz/cum were the 
product of preconceived ideas and the misinterpretation of certain 
facts. There are still a few observers who persist in seeing centro- 
spheres in the cells of higher plants, in which a score or more of the 
most competent cytologists, with the aid of the very best methods, 
have failed to find any such structures. It may be of some interest to 
note, however, that the centrospheres figured more recently by these 
observers are not drawn with the old-time diagrammatic distinctness, 
and it will probably not be long till these structures will not appear 
at all in figures illustrating karyokinetic phenomena in Ad/cum cepa 
and species of Lilium. 
