176 Mottier.—Nuclear and Cell Division 
and later no polar radiations were seen, or only a very few. 
The rod-shaped centrosomes were, however, always present 
(Figs. 19, 20, 21). In some cases observed, when the daughter 
nuclei were provided with membranes, the centrosomes pos¬ 
sessed a few faint polar radiations (Fig. 22). The chromo¬ 
somes are short, bent, slightly U-shaped, and about thirty-two 
in number. They lie closely crowded together, so that 
counting is difficult, and the number could not be exactly 
ascertained. 
Regarding the body which is known as a centrosome among 
the Brown Algae, the old questions of morphological unity 
and phylogenetic origin still present themselves. It is not 
my purpose, however, to go into the voluminous literature 
touching upon these and similar questions, nor to discuss the 
various and conflicting theories that have been advanced from 
time to time. I shall content myself with a brief presentation 
of the facts as I have observed them in Dictyota and as they 
are known in Fucus and the Sphaceleriaceae. 
In the young tetraspore mother-cells of Dictyota , before 
they have increased noticeably in size, no centrosomes with 
their characteristic radiations were seen, nor were any ob¬ 
served in vegetative cells showing no sign of karyokinetic 
activity. 
Throughout the two divisions in the tetraspore mother- 
cells the centrosome is unquestionably present at all stages, 
and in the germinating tetraspore and the first three or four 
cell-generations of the seedling plant resulting therefrom, 
the persistence of this body is undeniable. In Fig. 23 is 
shown a tetraspore which has begun to germinate. The 
structure of the nucleus itself does not indicate any karyo¬ 
kinetic activity, and we may say that it is in the resting 
condition, but the very evident centrospheres are in the 
position of the future poles of the spindle. The centrosomes 
are also rod-shaped, and, as elsewhere, can be seen with the 
greatest clearness. A daughter nucleus resulting from the 
first division in the spore is shown in Fig. 24. The same 
may be said of the next two or three successive generations 
