No. 460.] STUDIES ON PLANT CELL.— V. 241 
cate that such structures have not come from the blepharoplast. 
Williams’ (:04b) recent work on Dictyota, while incomplete in 
the series of stages illustrating the fusion of gamete nuclei (fer- 
tilization), presents a very interesting comparison of the devel- 
opment of the first -cleavage spindle in fertilized eggs with 
parthenogenetic eggs. In the fertilized egg there is regularly 
found a centrosphere which apparently divides into two that 
separate until they lie at opposite poles of the mature spindle. 
*In the parthenogenetic egg, on the contrary, the spindle is mul- 
tipolar and develops very irregularly from a kinoplasmic mesh 
which is intranuclear and there is no sign of centrospheres. 
Williams believes that fertilization enables the fusion nucleus 
to form de novo a centrosphere external to itself which is not 
possible for the nucleus of a parthenogenetic egg. 
It should be noted that these conclusions are all against the 
view that the centrosome is a permanent organ of the cell and 
that the blepharoplast holds any direct relation to centrosomes 
when present in the first cleavage spindle and inferentially rather 
strengthens the doubt that the blepharoplast is derived from a 
centrosome, which point was discussed in our account of the 
sperm in Section III. However, Ikeno (:04) in a paper which 
arrived too late to be treated in Section III, is very positive that 
blepharoplasts are centrosomes, presenting his evidence clearly, 
but his explanation of the conditions under which blepharoplasts 
are formed from the plasma membrane does not seem to me con- 
clusive, especially in the light of Mottier's (: 04a) recent paper on 
Chara, which also could not be treated in Section III (see Amer. 
Nat., vol. 38, p. 576, 1904). 
3. Asexual Cell Unions and Nuclear Fusions. 
As stated earlier in the paper, the test of a sexual act must 
lie with the history of the elements which unite, unless we 
choose to treat sexuality as a purely physiological process and 
disregard its relation to morphology in ontogeny and phylogeny. 
This relation is so precise, 7. e., sexuality is so firmly established 
as a fixed period in the life history of most organisms, that the 
biologist generally thinks of the sexual process as a part of the 
