466 JOURNAL OF SCIENCE. 
like stigma stands at the mouth of the corolla tube, while the stamens 
are placed near the bottom; in the other the stamens are at the 
mouth of the corolla, while the stigma is near the bottom of the tube. 
If a moth visit the first form, it gets some pollen on the further end 
of its proboscis while sipping up the nectar, and in going to the latter 
form it leaves this on the button-like stigma. At the same time it 
gets a fresh supply of pollen on the front of its head, which it leaves 
on the stigma when visiting the long-styled form. The correctness of 
this view has been proved experimentally by Darwin, who showed 
conclusively that Primulas legitimately cross-fertilized produced large 
capsules with numerous and fine seeds, those fertilized illegitimately 
gave smaller capsules with fewer and smaller seeds, while those self- 
fertilized either produced no seed at all or very imperfect ones. 
Some flowers, especially of the genus Lythrum or Loosestrife, have 
their stamens and stigmas at three different heights, perhaps to suit 
three kinds of insects. 
Besides dichogamy and heterostylism which I may term 
generalised modes of ensuring separation of the reproductive organs, 
there are innumerable special modes of securing the same object, but 
their very number and speciality precludes my doing more than men- 
tioning afew of them. Thus in a very large number of flowers the 
relative position of the stigma and anthers are such, that self-fertiliza- 
tion is impossible. This is the case in such a number of plants, 
belonging to so many orders in every large group, that it is almost 
impossible to mention them except in detail. The maximum degree 
of differentiation is probably reached in the Orchidece, and one of the 
. most interesting works written by Darwin was entirely occupied with 
a description of the modes in which fertilization of the flowers of this 
wonderful order is accomplished. Without specimens,- however, or 
diagrams, a bare description of any of these would be uninteresting. 
The Asclepiadec have reached an almost equal degree of specialization ; 
and by simpler means the same end, viz., the impossibility of self- 
fertilization has been attained by an immense number of plants 
belonging to the following, among other orders, Ranunculacee, Gera- 
nmiacee, Leguminose, Composite, Scrophularinee, Labiate, &e. I will 
just mention one of the devices which have been developed in different 
parts of different flowers with this end in view, namely irritability. 
In all Barberries, the stamens stand well out from the pistil when the 
flower first opens, but if anything touches the base of a stamen it 
springs up to the middle of the flower. This device is not of course 
for the purpose of placing the pollen on its own stigma, but to brush 
it on to the head of the insect, whose intrusion has been the cause of 
irritation. In the genus Mimulus (to which the musk plant belongs) 
the stigma is irritable. It consists of two plates which le in the | 
opening of the corolla tube, and the lower of which, if touched, closes 
up against the upper, exposing the stamens to view. If pollen has 
been brushed on to the lower lobe, then after it has once closed up it 
does not open again. If however it has only been touched and no 
pollen left on it, it quickly recovers from its irritation and opens out 
once more. But again the maximum degree of differentiation is 
reached among Orehids. In the genus Catasetum a portion of the 
flower is modified into what Darwin terms an antenna, which projects 
in such a manner as to come into contact with any insect visiting the 
