rilK I'Kiri'lLlSA'l'lON ol' I'1J)\VKK.S i;V INSECTS. 
105 
reach it on arriving :it the hottoni of the corolla tube ; and if special 
marks, the so-called " guides," bo on the corolla, they invariably indicate 
the right direction to the store of honey. 
All these correlations meet the two ends — viz. of supplying the insect 
with food, and that the latter should pollinate the stigmas. They conse- 
quently necessitate some common cause to account for them. And since 
there is no known external agency other than the insect itself, it is a fair 
d priori assumption that such, in some way or other, has been the actually 
inciting cause of the floral irregularities. Let us take, for example, the 
calyx of Salvia. It is two-lobed, and if we examine the position of the 
" cords," they are found to be arranged as foUows : — 
d 
d d 
m m 
m 711 
d d 
711 m 
s 
It is, of course, composed of five leaves, each has a midrib or dorsal 
cord (d). The margins properly have none, but in the united state of a 
gamosepalous calyx one, at least, is run up where the edges cohere {m). 
These we may call marginal cords. But now additional ones are present. 
Instead of there being one only, two are added on each side, where the 
tendency to split the calyx occurs. Again two are added in front, while 
here a supernumerary cord (s) lies between them — exactly where the 
greatest strain is felt. 
The explanation is simple. An insect alights on the corolla-lip, its- 
whole w^eight is to the fore : this bears down upon and presses against 
the calyx tube, tending to stretch it in front. To meet this strain Nature 
has cunningly run up little girders exactly where an engineer would have 
placed them, especially round the anterior half of the calyx, where the 
strain is greatest. 
This power of responding to external strains is universally to be seen 
in plants. It is a property of living protoplasm. It is well seen in 
climbing plants, and can be shown by experiment ; for if a growing shoot 
or petiole be weighted so as just not to break it, in a few days it will 
be found capable of supporting much greater weights than it would 
naturally be able to bear. 
Self-fertilising Flowers. — If a conspicuous insect-loving flower 
cease to receive its visitors it ceases to secrete honey, and its corolla 
becomes reduced in size ; in fact the flower may altogether cease to open 
its flower-buds. Such is the origin of the so-called cleistogamous 
flower-buds — a word signifying "concealed unions." Such may be easily 
seen on Violets below the leaves during the summer. 
Wind-fertilised Flowers. — With regard to these they appear, in 
the majority of cases (excluding Fir trees and their kin), to be degradations^ 
but have become adapted to receive the pollen from other flowers by the 
agency of the wind. They are often unisexual, as the Nettle, Sorrels, and 
in most cases the stigmas are large and often feathery, so that they readily 
catch the pollen, as in Grasses, Burnet, Saxifrage, &c. 
