1899] ASEXUAL NUCLEAR FUSIONS 239 
Asexual Nuclear Fusions. 
Fusion of nuclei, whether it accompanies the union of so-called sexual 
cells, or occupies a position in the life-history which apparently denies 
it that dignity, must for some time remain a subject of absorbing 
interest, not only on account of its complexity, but also owing to the 
important biological questions involved. 
Professor Percy Groom draws attention in a recent paper (Zvrans. 
Got. Soc. Edin. 1898-99, pp. 132-144) to the number of such fusions 
of other than a distinctly sexual character, which we now know to 
occur in the vegetable kingdom. 
Among fungi, in the Uredineae and Ustilagineae, the union takes 
place in the teleutospore, which, originally binucleate, contains but one 
nucleus at the period of germination, when it gives rise to the short 
sporidium-bearing promycelium. In Proto- and Autobasidiomycetes 
the fusion takes place in the homologue of the teleutospore, viz. the 
young basidium, which, when mature, represents, according to Brefeld, 
the Uredine promycelium, and bears basidiospores. Finally, in Ascomy- 
cetes the same phenomenon may be observed in the young ascus, which 
de Bary regards as a reduced sporophytic generation parasitic on the 
parent plant. Apart from fungi similar nuclear fusions are only 
known to occur among Angiosperms, where the union of two polar 
nuclei in the embryo sac precedes the formation of the endosperm, 
which, by the way, we are pleased to see the Professor regards as 
homologous with that of Gymnosperms, and consequently with the 
prothallus of the lower forms, its appearance having been postponed 
owing to functional degeneration. These fusions are thus always 
interpolations, and distinctly asexual in character, as is shown by 
the position they oceupy in the life-history of such forms as the 
Ascomycete Sphacrotheca and the Angiosperms, in both of which the 
union takes place along with and subsequent to a well-marked sexual 
act, viz. the union of the antheridial and oogonial nuclei in the former, 
and that of the nuclei of the pollen-tube and egg-cell in the latter. 
In every known case they take place in a portion of the life-history, 
which has undergone degeneration, and which is at the same time 
fructificative in development, as well as frequently parasitic in 
character and sometimes at least homologous with the host plant (?). 
Professor Groom suggests that if this fusion can be taken as 
evidence of vegetative degeneration in one segment of the life cycle, 
it may be possible to employ it as a means of distinguishing between 
antithetic and homologous alternation of generations among plants; but 
whatever be the physiological rationale of such fusions—and an 
adequate explanation seems still far to seek—they appear to have 
much in common with the similar phenomena which constantly accom- 
pany the union of sexual cells, and both will in all probability be 
ultimately found-to perform similar functions in the life of the plant. 
