126 LIVERPOOL BIOLOGICAL SOCIETY. 
of his elaborate essay On the Self-fertilisation of Plants* he 
summarises the results he has arrived at in the following 
words :— 
“So far from there being any necessarily injurious or 
evil effects resulting from the self-fertilization of plants in 
a state of nature, they have proved themselves to be in 
every way the best fitted to survive in the creat struggle 
for life.” 
The Orchidacez are frequently appealed to as a typical 
group where the phenomena of “cross-fertilization”’ are 
particularly well seen. On the other hand certain species 
belonging to the genera Ophrys, Habenaria, Dendrobium 
and others are mentioned by Darwin himself as being 
adapted for “‘ self-fertilization”’; and the investigations of 
Forbes + demonstrate that even in this group, so greatly 
modified in many cases to bring about ‘‘ cross-fertilization ”’ 
the Knight-Darwin Law has many and important excep- 
tions. 
Must we then throw overboard our belief in the neces- 
sity for ‘‘ cross-fertilization”’ as a law of nature so far as 
the plant world is concerned, or retain it so modified or 
loaded with exceptions as to render it doubtful whether it 
be a law at all? There are two obvious considerations 
which must be taken account of before answering this 
question. The first of these is what do we understand by 
the phrases, “‘ cross-fertilization ”’ and “‘self-fertilization”’? 
I believe that the diversity of opinion on this question is 
in reality due to an inaccurate use of these terms. The 
second point, to my mind of even more importance, is 
that in the discussion of the subject appeal has been made 
to one only of the two sub-kingdoms of the Plant world. 
*Linn. Soc. Trans. 2 Ser. Bot. vol. 1., p. 396. 
+On the Contrivances for ensuring Self-fertilization in some Tropical 
Orchids. Linn. Soc. Jour. Bot. xxi., p. 538: 
