464 TROPICAL NATURE IX 
way caused the pollen to stick to some part of its body, 
which was always the exact part which the insect, on visiting 
another flower, would bring in contact with the stigma, and 
thus fertilise it. These investigations explained a host of 
curious facts which had hitherto been facts only without 
meaning, such as the twisting of the ovary in most of our 
wild orchids, which was found to be often necessary to bring 
the flower into a proper position for fertilisation,—the exist- 
ence of sacs, cups, or spurs, the latter often of enormous 
length, but shown to be each adapted to the structure of 
some particular insect, and often serving to prevent other 
insects from reaching the nectar which they might rob with- 
out fertilising the flower,—the form, size, position, rugosities, 
or colour of the lip, serving as a landing-place for insects and 
a guide to the nectar-secreting organs,—the varied odours, 
sometimes emitted by day, and sometimes by night only, 
according as the fertilising insect was diurnal or nocturnal, 
and other characters too numerous to refer to here, so that it 
became evident that every peculiarity of these wonderful 
plants, in form or structure, in colour or marking, in the 
smoothness, rugosity, or hairiness of parts of the flower, in 
their times of opening, their movements, or their odours, had 
every one of them a purpose, and were, in some way or other, 
adapted to secure the fertilisation of the flower and the pre- 
servation of the species. 
Researches on the Cowslip, Primrose, and Loosestrife 
The next set of observations, on some of our commonest 
English flowers of apparently simple structure, were not less 
original and instructive. The cowslip (Primula veris) has 
two kinds of flowers in nearly equal proportions: in the one 
the stamens are long and the style short, and in the other the 
reverse, so that in the one the stamens are visible at the 
mouth of the tube of the flower, in the other the stigma 
occupies the same place, while the stamens are half-way down 
the tube. This fact had been known to botanists for seventy 
years, but had been classed as a case of mere variability, and 
therefore considered to be of no importance. In 1860 Darwin 
set to work to find out what it meant, since, according to his 
views, a definite variation like this must have a purpose, 
