Dec. 1898. ] BOTANICAL SOCIETY OF EDINBURGH. 135 



sexual activity, also the formation of sexual organs, and 

 even of physiologically associated organs. This tendency 

 suggests that the sexual act, with its nuclear fusion, is 

 correlated with the inhibition of vegetative activity, and is 

 calculated to atone for it, both in the race and in the 

 individual. The physiological question therefore arises, 

 "" Do the nuclear fusions under discussion, in this respect, 

 bear any analogies to the sexual act, and are they associated 

 with any vegetative degeneration ? " 



Answering at the same time both tliese questions, 

 morphological and physiological, the follovving general 

 <;onclusions seem probable in reference to the nuclear 

 unions occurring in the ascus, in the basidium, in the 

 spores of Ustilaginei\3 and Uredineiij, and in the embryo-sac 

 of Angiosperms : — 



1. The nuclear union does not represent a true sexual 

 act ; it is an interpolation. 



2. It takes place in a small generation which is fructi- 

 ficative in development. 



3. The generation in which the nuclear fusion occurs is 

 probably degenerate in all cases, and it is natural to suppose 

 that the fusion is correlated with the vegetative degeneracy. 



4. In some cases the nuclear union occurs at the actual 

 inception of the generation, and possibly in all cases it 

 occurs at a stage which represents the inceptive stage of 

 the earliest phylogenetic condition of the generation in its 

 particular class. The nuclear union takes place in some 

 cases, and possibly in all cases, inside a cell which is 

 actually or phylogeneticly a single spore. 



The succeeding pages are taken up in an attempt to 

 prove these conclusions in detail. 



Angiosperms. — The nuclear union takes place in the 

 gametophyte generation, which has lost its power of leading 

 an independent existence, and which is reduced to a mere 

 fructificative individual parasitic upon, and symbiotic with, 

 its predecessor. So far as is known, the nuclear fusion 

 occurs neither among Gymnosperms nor in those Angio- 

 sperms whose prothallia (endosperms) develop before 

 fertilisation ; it is limited to those flowering plants in 

 which the female prothallium is so degenerate, and in such 

 physiological harmony with its parent, as to develop to a 



