274 FERTILIZATION OF FLOWERS BY INSECTS. 
principal applications of the foregoing thesis in the explanation of 
the forms and properties of flowers. 
If it is true that intercourse between distinct individuals produces 
a more vigorous and numerous offspring, it is equally true that 
every variation in the flowers which favors the transfer of pollen 
from one individual to another secures a notable advantage to the 
individual in which it takes place, and therefore cannot fail to be 
fixed and perpetuated by means of natural selection. 
Now, as far as we know, there are only two external agents 
which can effect this transfer, namely, the wind and insects ;— 
naturally with the contingence of very different floral structure.* 
The different species of plants, as concerns the variations which 
first appeared in them, would, by natural selection, accommodate 
themselves to the wind or the visits of insects, by suitably model- 
ling their flowers either upon an anemophilous or an entomophilous 
type.t The action of the wind is simple and uniform, while that 
of insects is extremely varied: therefore their self-adaptation to 
the action of the wind presupposes a variation in a single and 
definite direction ; whereas that to the visit of insects takes place 
in as many different ways as there are differences between individ- 
ual insects; that is to say, differences in size, form, structure, | 
habits, modes of life, sympathies, antipathies, seasons, etc. There- 
fore, from the Darwinian point of view, we should expect to find : 
first, that the variations of plants arising from adapting themselves 
to the multiform actions of insects should have taken place far 
more frequently than those due to their adapting themselves to the 
uniform action of the wind ; second, that plants modified to receive 
* mh p a + 3 
1 by me in this field of biological study put me in 
littl hat tł y Th he feeu undating agents 
of irra kaen insects and th e wind I 
The hum bir ah sag Ornismya, Pipa pee a 2 for a great variety of 
tropical ne snails for Rhodea Ji ica and some Aro water for Vallisneria 
spiralis, probably for all ie asteka. and all the Plorides patie ee to the recent 
and beautiful observations of Thuret and Bornet). 
As to humming birds, ne ble to pical countries I was obliged 
to limit myself to conjectures, which have subsequently been partly confirmed by let- 
from Charles Darwin as regards the fecundation of the genus Strelitzia, and from 
Fritz Miiller as regards that of certain Passiflore, Salviæ and other Brazilian plants. 
The 
4 
ternas befrutkning oy ada 1869) and by some others. That is why I permit 
to translate with such words the compound -a Wind-blüthen and Insect-bl 
used by the author, which cannot be literally translated. 
