Insects and Flowers 
569 
bees, who use pollen not only directly themselves, but carry it in quantities 
to their nests as food for their young, and in the case of honey-bees for the 
other workers busy indoors. To show the affinities and the number of 
species of the insect visitors to entomophilous flowers I have compiled the 
following figures from Robertson’s records of his observations on flowers 
in the neighborhood of Carlinville, Ill. In twenty-six observing days 275 
insect species visited the flowers of Pastinaca saliva , of which 1 was a Neurop- 
teron, 6 were Hemiptera, 9 were moths and butterflies, 14 were beetles, 72 
were Diptera, and the rest Hymenoptera, of which 21 were bees, 39 saw- 
flies and parasitica, and the remainder wasps, solitary and social. Of 115 
species visiting the milkweed Asclepias verticillata, 52 were Hymenoptera, 
42 Diptera, 16 Lepidoptera, and 3 Coleoptera; of 52 species visiting Rham- 
nus lanceolata , 23 were various solitary bees; of 87 species found at the 
flowers of the willow Salix cor data in seven days, 43 were Hymenoptera, 39 
Diptera, 4 Coleoptera, and 1 Hemipteron; 112 species of insects visited Ceano- 
thus americanus in five days; 79 species visited sweet-clover in two days; 
71 species visited the little spring beauty, Claytonia Virginica, in twenty-six 
days, while 18 species visited the yellow violet in seven days. The hive- 
bee and the bumblebees are the pre-eminent cross-pollinating insect agents, 
some flowers, as clover for example, having its pollen distributed by bumble¬ 
bees alone (although Robertson found 13 different species of butterflies rob¬ 
bing nectar from red clover). The willow Salix humilis , watched for eleven 
days, had its staminate flowers wholly monopolized by honey-bees, although 
51 kinds of nectar-feeding insects visited its pistillate flowers. Of the 488 
species of American entomophilous flowers which have been studied by 
Robertson I find by going through his records that the honey-bee visits nearly 
all, while bumblebees are recorded from a large number. 
The adaptations for pollen-gathering are mostly limited to bees and 
consist of (a) the development of hairs, simple and branched or feathery, 
specially situated to brush up and hold the pollen grains as the bee clambers 
over the stamens, and (b) in the honey-bees and bumblebees the develop¬ 
ment of the well-known pollen-basket, or corbiculum (see description and 
figure on p. 528). The adaptations for nectar-drinking consist in the elon¬ 
gation and tube-forming modification of the mouth-parts of bees, flies, and 
moths and butterflies. While in the less specialized bees the mouth-parts 
are short, with the labium in the condition of a short broad flap-like lip 
(Fig. 716), in the specialized nectar-drinkers, as the bumbles, the hive-bee, 
and the other so-called long-tongued forms, the maxillae and labium are 
long and slender and the various parts can be so held together as to form a 
very effective lapping and sucking proboscis (Fig. 717). Similar conditions 
exist among the two-winged flies (Diptera); the proboscis of a flower-fly 
(Syrphid) or bee-fly (Bombiliid), for example, is a long, slender, sucking beak 
