PREFATORY NOTICE. ix 
visited at night by any of the innumerable individuals of the many 
species of minute moths. <A lepidopterist while collecting at 
night, if endowed with only a small portion of the indomitable 
patience displayed by Miiller, could ascertain this fact. The 
question possesses a considerable degree of theoretical interest ; 
for if these inconspicuous flowers are never visited by insects, why, 
it may be asked, do they expand, and why is not the pollen 
protected by the petals remaining closed, as in the case of 
cleistogamic flowers? It would perhaps be possible to smear 
such small flowers with some viscid matter, and an examination 
of the petals would probably reveal nocturnal visits by moths by 
the presence of their scales; but it would be necessary to prove 
that the matter employed was not in itself attractive to insects. 
H. Miiller gives long lists of the several kinds of insects which he 
has seen visiting various flowers in Germany; and it would be 
interesting to learn whether the same insects and the same pro- 
portional number of insects belonging to the different orders, visit 
the same plants in England as in Germany. 
There are many other subjects which it is desirable that some 
one should investigate, for instance, by what steps heterostylism 
(of which an account will be found in the present work) originated : 
and with trimorphic heterostyled plants we meet with a more 
extraordinary and complicated arrangement of the reproductive 
system than can be found in any other organic beings. In order 
to investigate this subject and several others, experiments in 
fertilisation would have to be ‘tried; but these are not difficult 
and would soon be found interesting. For instance, there are 
some plants, the pistils and stamens of which vary much in length, 
and we may suspect that we here have the first step towards 
heterostylism ; but to make this out, it would be necessary to test 
in many ways the power of the pollen and of the stigma in the 
several varieties. There exist also some few plants the flowers of 
which include two sets of stamens, differing in the shape of the 
anthers and in the colour of the pollen; and at present no one 
