CROSS- AND SELF-FERTILIZATION AMONG PLANTS. 127 
The essential feature in the process of fertilization is 
the fusion of the nuclei of the male and female reproduc- 
tive cells. Self-fertilization must then mean the fusion of 
the nuclei of male and female reproductive cells, these 
cells being produced on the same individual. In other 
words self-fertilization involves hermaphroditism. Cross- 
fertilization on the other hand must mean the union of 
the nuclei of male and female reproductive cells, where 
- these cells are produced in reproductive organs on separ- 
ate individuals. Cross-fertilization does not of course 
necessitate unisexuality; two hermaphrodite individuals 
may fertilise each other, and in proterandrous and protero- 
gynous forms cross-fertilization must of necessity take 
place. 
To'take instances. The fertilization of the ‘ archicarp’ 
of Hurotium aspergillus-glancus by the ‘ pollinodium’, both 
of which are borne by the same hypha, is an undeniable 
instance of self-fertilization. The fertilization of the ovum 
of the dicecious Alga Fucus vesiculosus by the sperm is in 
like manner an undeniable instance of cross-fertilization. 
Again the fertilization of the ovum of the hermaphro- 
dite prothallus of a typical member of the Polypodiaces 
by the sperm (antherozoid) (assuming that the prothallus 
is not proterandrous) may be considered as an example 
of self-fertilization. In the case of certain members 
of the Osmundaceze where the prothallus is dicecious, 
the union of the sperm and ovum must be considered 
as a case of cross-fertilization. Manifestly, it follows 
that among the Heterosporous Pteridophyta cross-fer- 
tilization must be of absolutely universal occurrence, 
since the contents of the microspore and megaspore 
correspond to male and female prothalli respectively, 
though greatly reduced in size and feebly different- 
iated. Once accept this conclusion I see no way of 
