EECEIs^T OBSEKYATIONS ON THE FERTILISATION OF PLANTS. 343 
search for honey and for pollen. We have already seen several 
instances of the mode in which insects, and especially those 
furnished with a long proboscis and belonging to the orders 
Lepidoptera and Hymenoptera, involuntarily detach some of 
the pollen while obtaining their food, and carry it away with 
them to fructify other flowers which they then visit. One of 
the most interesting examples of this was flrst described in 
detail by Darwin in his work on the Fertilisation of Orchids ; 
and it is extremely easy to observe the manner in which the 
pollen-masses or “ pollinia ” of orchids are carried away on the 
proboscis of butterflies and moths. The natural order Ascle- 
piadacese, to which belong the beautiful waxen-flowered Hoy a 
and the singular foetid Stapelia, has the pollen arranged, in the 
same manner as in orchids, in pollen-masses which are similarly 
flxed in pairs to a viscid base, the whole apparatus being easily 
detached on to any insect which visits the flower. Fig. 3 repre- 
sents the foot of a butterfly with eight of these pollen-masses 
and eleven of the viscid bases attached to it, belonging to the 
Brazilian Asclejpias cwrassavica. 
The second mode in which insects assist in the fertilisation 
of flowers is by the voluntary deportation of pollen ; and this 
is chiefly effected by Hymenoptera belonging to the class 
Apidse, which includes the hive and bumble-bees that build 
nests in which they store up large quantities of food for their 
young while in the larva state. This “ bee-bread,” as it is 
termed, with which the thighs of homeward-bound bees are 
seen to be heavily laden, consists almost entirely of innumerable 
pollen-grains robbed from the flowers, which the little depre- 
dators may be seen to despoil in a very scientific manner. 
Though the greater quantity of this pollen is carried home, 
small quantities of it are unintentionally left behind here and 
there on the stigmas of the flowers, quite sufficient to ensure 
the fertilisation of the ovules. Prof. Muller arranges the 
different genera of Apidse into a series according to their 
adaptation for this deportation of pollen, from the extent to 
which their thighs, shins, and feet are clothed with hairs. 
Fig. 4, (X, is the right hind- leg of the little Prosopis variegata, 
in which the upper part of the leg is perfectly naked, the lower 
portion only being slightly covered with hairs (and this is even 
somewhat exaggerated in the drawing) ; so that its power of 
collecting pollen is very small. Fig. 4, 6, is the same limb 
of a neuter or working individual of a species of Bombus or 
bumble-bee, in which every part of the leg is densely clothed 
with hairs, and the quantity of pollen it can carry off is there- 
fore immense. 
Besides these, there is a third purpose for which insects 
remove the pollen of flowers, which is less known, and the 
