364 Mr. Blackman and Miss Fraser. Sexuality and [Oct. 31, 



also be explained by the fact that a reduced fertilization in the ascogonium 

 was overlooked. 



Exact data as to the nuclear behaviour of Ascdbolus furfuraceus in its early 

 stages of ascocarp development will be of special interest. It would seem 

 likely that the nuclei fuse in pairs when they meet, as described by Harper (16), 

 in the large ascogonial cell which gives origin to the ascogenous hyphse. One 

 of Harper's figures shows these nuclei in very close contact. 



It is possible, also, that the parthenogenesis in other forms, in which 

 a ccenogamete develops without the intervention of a male organ (e.g., the 

 Mucorini and Saprolegniaceae), may be explained in the same way, by 

 a fusion, in pairs, of the female nuclei,* and so not be a true parthenogenesis. 



The fusion in the ascus still remains a most puzzling process, for which, at 

 present, no explanation is forthcoming. That it is not a substitute for the 

 ordinary sexual process, nor a nuclear fusion which has been shifted, in 

 descent, from the ascogonium to the ascus, as Dangeard and Kuyper believe, 

 is clearly shown (apart from such forms as Pyronema, Boudiera, etc.) by 

 H. granulata, where, even in the absence of the autheridium, the fusion in 

 the ascus is preceded by a fusion in the ascogonium. On the other hand, 

 the curious simultaneous division of the two nuclei at the time of ascus 

 formation — whether the ascogenous hypha bends over at the apex or whether 

 it remains straight, as in Galactinia succosa — seems only to be explained as a 

 method of ensuring that the fusing nuclei are separated in descent by at 

 least one division. Now, such a separation, in descent, of the fusing nuclei 

 is, as far as we know, an attribute of sexual fusions alone (though in many 

 fusions which are accepted as sexual, the degree of relationship is very close). 

 We have thus two closely related fusions, one of which is obviously a sexual 

 fusion, while the other, in one character at least, partakes of a sexual nature- 

 A satisfactory solution of the difficulty of the dual fusions can hardly be 

 expected till we know the number of chromosomes throughout the life-history 

 of some ascomycete. 



That there is a definite alternation of generations in the life-history of 

 Ascomycetes which possess an ascogonium seems very probable. The 

 ordinary vegetative mycelium would appear to be the gametophyte, which 

 bears the ascogonium, and antheridium if present, while the products 

 of fertilization, the ascogenous hyphae (which are parasitic on the 

 gametophyte) and the asci, represent the sporophyte. The countings of 

 chromosomes are, however, too few and too unsatisfactory to allow of 



* Kuyper (21) has independently made a similar suggestion in the case of the 

 Saprolegniaceae, and has even suggested that the figures of Davis (11) on egg development 

 in Saprolegnia support the view of a nuclear fusion. 



