134 TRANSACTIONS AND TROCEEDINGS OF THE [Sess. lxiii. 



the ascus after the coaleseeuce of its two nuclei. Harper 

 further states that the young ascus of Pcriza Stevcnsoniana 

 contains four nuclei, which, after uniting in pairs, coalesce 

 to form a single nucleus. "Whether or no we accept 

 without confirmation Harper's views as to the source of 

 the two nuclei in the ascogonium of Sphacrotlieca, his 

 researches render it well-nigh impossible to suppose that 

 the fusion of the two or four nuclei in the young ascus is 

 a true sexual act. 



It is, in fact, evident that if we regard the union of the 

 nuclei in the young ascus, or in the young embryo-sac, as 

 being morphologically sexual, that is, homologous with the 

 sexual act of the sexual ancestors of these plants, we are 

 involved in a number of improbable and conflicting assump- 

 tions. 



Still, between the sexual act and these obscure nuclear 

 fusions in the fungi named, and in the Angiosperms, there 

 is one strong resemblance in that the act involves the 

 union of a definite and constant number of nuclei prepared 

 in a definite manner. Does the analogy go any further ? 

 If, for a moment, we regard the sexual act as a mere 

 morphological phenomenon, one obvious fact appeals to us, 

 that it takes place at a definite stage in the life-history, 

 namely, the inceptive stage of the individual. The sexual 

 union, involving a fusion of two nuclei, brings with it a 

 break in the life-history of the individual ; whereas a mere 

 cytoplasmic union in the higher fungi and vascular plants, 

 at least, is accompanied by no such interruption. Hence 

 the morphological question arises, " Do the nuclear fusions 

 under discussion occur at a definite stage in the life-history 

 of a plant, and, in particular, do they mark the inception 

 of a new generation?" On the other hand, if we regard 

 the sexual act as a ])hysiological phenomenon, the fact that 

 the higher forms of plants and animals are, with a few 

 suggestive exceptions, sexual, is sulllcient evidence of the 

 stimulating influence on the race of the sexual act, and 

 presumably of the associated nuclear union. Furthermore, 

 there is a general tendency, exhibited both in classes and 

 in individuals, towards an inverse proportion between, 

 on the one hand, vegetative vigour and circumstances 

 favouring vegetative growth, un<l, on the other hand. 



