576 Wager. — The Sexuality of the Fitn°i. 
consists in the definite fusion of a male nucleus with a female 
nucleus to form the primary nucleus of the embryo or new 
generation.’ 
In the higher groups (the Ustilagineae, Uredineae, Asco- 
mycetes, and Basidiomycetes) the question of their sexuality 
has recently been brought prominently forward by the dis- 
covery that in certain of their cells a fusion of nuclei takes 
place at a period just antecedent to, or during, the formation 
of spores, which is regarded by some observers as a true 
sexual process, and which in some respects certainly does 
appear to take the place of, and produces the same results as, 
the ordinary phenomena of sexuality. 
In the following pages I propose to deal first of all with 
the phenomena of fertilization occurring in the lower Fungi, 
secondly with the nuclear fusions in the higher Fungi, and 
thirdly with some theoretical considerations concerning the 
phenomena of sexuality and nuclear fusion in the whole group. 
Phycomycetes. 
The Peronosporeae 1 exhibit a distinct sexual differentiation 
in the formation of male and female elements in distinct cells, 
oogonia (ooangia) and antheridia. The oogonium is pro- 
duced as a terminal or intercalary swelling on a hyphal 
filament inside the host-plant. The antheridium is a tubular 
outgrowth which may be formed on the same filament as the 
oogonium or on another one in its immediate neighbourhood. 
Both contain protoplasm and numerous nuclei. The anthe- 
ridium comes into contact with the oogonium, and curves 
closely around it. The nuclei of the oogonium, and probably 
of the antheridium, then divide by a process of karyokinesis 
each into two, so that there are now twice as many. The 
contents of the oogonium separate into two distinct parts — 
a peripheral portion (the periplasm), which contains all the 
nuclei, and a central spherical portion (the gonoplasm), which 
1 Wager, Ann. Bot., iv, 1889, and x, 1896; Berlese, 'Jahrb. f. wiss. Bot., 
Bd. xxxi. 
