152 
V. H. Blackman. 
unicellular organisms, for the two conjugating individuals would 
very likely be far separated in descent and would probably have 
spent their lives under slightly different conditions. 
Although these, apparently primitive, results of fertilisation are 
still retained in the typical process, as observed in the higher orga¬ 
nisms, yet there are to be found in animals and plants a series of 
reduced processes in which one or more of these characteristic 
results of fertilisation have been lost. The first step in such a process 
of reduction would seem to be the union of gametes more or less 
closely related in descent, so that fertilisation no longer brings about 
the mingling of different hereditary properties. There are many 
examples in plants, from “self-fertilisation” in Angiosperms to the 
union of gametes of the same brood among the Thallophyta. 
“Self-fertilisation” among Angiosperms is no doubt a reduced 
process for the primitive forms would seem to have been cross-polli¬ 
nated by the wind. It is, of course, not a process of true self¬ 
fertilisation, for it is not a fusion of gametes derived from the 
same individual, but merely that of gametes derived from 
distinct gametophytes, which, however, take their origin from, 
and are enclosed within, the same sporophyte. A process of true self¬ 
fertilisation is, of course, impossible in plants which are lietero- 
sporous ; it does, however, appear sometimes to occur in homo- 
sporous forms such as Osmunda and Ceratopteris, 1 and seems to be 
found in such animals as the Trematoda. 
A large number of cases of close in-breeding are to be found in 
the Phycomycetes amongst the fungi, where the sexual organs often 
arise on neighbouring cells or hyphae (e.g., Pcronospovaceae, Basi- 
diobolus) ; in Sphnerotheca and Pyronema among the Ascomycetes 
the sexual organs would also seem to arise on neighbouring hyphae 
on the same mycelium. In these cases there can be no mingling of 
ancestral characters and they are certainly to be looked upon as 
physiologically simpler types of fertilisation when compared with 
the more complex types in which there is a mingling of such 
characters. There is little doubt also that they are to be considered 
as reduced in evolution, when one considers the fact that these 
fungal forms are probably derived from algal ancestors in which the 
male elements were either motile or free-floating, and so had oppor¬ 
tunities of bringing about cross-fertilisation. The loss of freedom 
of the male cells in a land plant must almost of necessity lead to 
1 R. P. Gregory. Proc. Camb. Phil. Soc. XII. (1904), p. 433. 
