336 SCIENCE PROGRESS. 



the question at issue. In Cyst opus, however, the life history 

 of which was regarded by Celakovsky as corresponding to 

 antithetic alternation, the nuclei in the developing oospore 

 appear to possess twice the number of chromosomes present 

 in those of the vegetative thallus. Reduction apparently 

 takes place just before the division of the thirty-two nuclei 

 which proceed from the nucleus of the zygote. From these 

 about four times as many zoospores are produced. The 

 details of this last division are not known but the analogy 

 which it presents to tetrad division is obvious. 1 



The recent discovery of a sexual nuclear fusion pre- 

 ceding the formation of the fruit body of Ascomycetes has 

 raised anew the question whether these plants do not ex- 

 hibit an antithetic alternation. This has been discussed 

 by Harper 2 but a definite conclusion is prevented by the 

 absence of the necessary observations on the number of 

 chromosomes present in the nuclei of the hyphae before 

 fertilisation. 



While these facts regarding normal alternation appear 

 to be most readily explained on the antithetic theory, it 

 must not be forgotten that the phenomena of apogamy and 

 apospory show that the nuclear changes (which presumably 

 occur in these developments also) are not necessarily as- 

 sociated with the sexual fusion or spore formation. No- 

 thing is known of the behaviour of the nuclei in these cases 

 and it is unnecessary to discuss the question on a priori 

 grounds in this place since this has been fully done by 

 Strasburger 3 and Bower. 4 From this standpoint the case 

 of apogamy in Balanophora elongata 5 possesses especial 

 interest. The facts are briefly these. As the result of 

 division of the primary nucleus, four nuclei are present at 

 each end of the embryo sac. Three of these at one end be- 

 long to the ovum and the two synergidae. The entire egg- 

 apparatus and the four nuclei at the antipodal end of the 

 embryo sac abort, taking no further part in the develop- 

 ment. This proceeds from the polar nucleus at the egg- 



1 Wager, Berlese. 2 Harper. 3 Strasburger (2). 



4 Bower (11). 5 Treub(2). 



