5 82 
Insects and Flowers 
flowers would not be visited by insects unless they had some inducements 
more substantial to offer. These inducements are the pollen and, to the 
great majority of flower-visiting insects, the nectar. 
It is of distinct interest to note that no plants with colored flower-parts 
or special floral envelopes existed (in geological time) before the time of 
winged insects. The oldest fossil Angiosperms, monocotyledons as well 
as dicotyledons, are from the lower Cretaceous rock strata; in Tertiary times 
there was a great increase in the number and variety of the dicotyledons, 
and most of the present families were probably in existence in those times. 
Winged insects are known from Devonian rocks, and much more numer¬ 
ously from Carboniferous strata; but all these early Paleozoic insects belong 
to the lower more generalized kinds, which to-day take little part in cross¬ 
pollination. Not until Jurassic times did the higher orders appear, the 
Hymenoptera, Lepidoptera, and Diptera, which include the great majority 
of the cross-pollinating insect agents. Thus the insects which we know to¬ 
day as the pollen- and nectar-feeders, hence flower-visitors, began to be abun¬ 
dant coincidently with or a little in advance of the flowering plants. Recip¬ 
rocally helpful and mutually adapting themselves to the growing interrela¬ 
tion, the flies, bees, moths, and butterflies on the animal side and the 
dicotyledonous plants with varied flower-shapes, color, and pattern on the 
vegetable side have developed so successfully that in present times both 
flower-visiting insects and insect-attracting flowers have come to be the 
most specialized and notable members of each of their respective groups of 
organisms. 
