No. 460.] STUDIES ON PLANT CELL. V. 241 



cate that such structures have not come from the blepharoplast. 

 Williams' (: O4b) 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 (:O4) 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 (: O4a) 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, i. 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 



