158 Fertilisation , Apogamy and Parthenogenesis. 
gametophyte of an “apogamous” fern or in the aecidium of 
Phragmidhim have any other function than that of providing a suitable 
nuclear mechanism ; they also would then belong to the category 
of reduced fertilisations in which two out of the three obvious 
results of the normal process have beeh lost. It would seem that 
since a normal egg-cell is apparently unable to develop into a com¬ 
plete organism if it starts with the reduced number of chromo¬ 
somes—and since only a few animals and plants have evolved a 
method of development in which chromosome reduction is done 
away with—a process of nuclear fusion is still necessary in the life 
history of a number of organisms, although they appear able to 
dispense with the other results which are brought about by a 
typical exogamous fertilisation. 
The Fungi are very probably a group in which the metabolic 
need of “rejuvenescence” by fertilisation has ceased, or almost 
ceased, to be felt, probably, as Marshall Ward 1 2 has suggested, owing 
to their parasitism, heteroecism and general mode of life. In the 
lower forms the sexual cells are often of close blood relationship, and 
though in the higher forms more recent work has established the 
existence of nuclear associations and fusions, yet in all these cases 
(except perhaps the lower Ascomycetes) these processes are of such a 
reduced type 3 that they would seem to have little other function 
than that of doubling the number of chromosomes (or their 
equivalents) 
A study of these various types of fertilisation shows how almost 
impossible of definition is that process, for not only does it appear 
that the fusion or association of cells or nuclei ( syngamy ) may 
have very different effects in different organisms, but it has been shown 
that the sharply characterised process of exogamous fertilisation 
with differentiated sexual elements may be connected by a series of 
% 
processes of increasing degradation and simplification, with one 
which is nothing more than a peculiar form of somatic or sporo- 
phytic budding. 
1 Quart. Jour. Micros. Science XXIV. (1884), p. 262. 
2 In Uredineae, an association of closely related nuclei in the 
aecidium or also in the mycelium, with a later fusion 
in the teleutospore; in Rasidiomycetes, an association 
of nuclei, probably of neighbouring vegetative cells, with a 
later fusion in the basidium ; in the higher Ascomycetes, a 
fusion of closely related nuclei in the ascus. The lower 
Ascomycetes, however, are excessively puzzling, for in them 
there are apparently two successive fusions, one in the 
oogonium and one in the ascus- 
