ECOLOGY OF FLOWERS; POLLINATION 179 
212. Studies in Insect Pollination. — The student cannot gather 
more than a very imperfect knowledge of the details of cross-polli- 
nation in flowers without actually watching some of them as they 
grow, and observing their insect visitors. If the latter are caught 
and dropped into a wide-mouthed stoppered bottle containing a bit 
of cotton saturated with chloroform, they will be painlessly killed, 
and most of them may be identified by any one who is familiar with 
our common insects. The insects may be observed and classified 
in a general way as butterflies, moths, bees, flies, wasps, and beetles, 
without being captured or molested. 
Whether these out-of-door studies are made or not, several flowers 
should be carefully examined and described as regards their arrange- 
ments for attracting and utilizing insect visitors (or birds). 
213. Cleistogamous Flowers. — In marked contrast with 
such flowers as those discussed in the preceding sections, 
which bid for insect visitors or expose their pollen to be 
blown about by the wind, are certain fowers which remain 
closed even during the pollination of the stigma. These 
flowers are called cleistogamous and of course are not cross- 
pollinated. Usually they occur on plants which also bear 
flowers adapted for cross-pollination, and in this case the 
closed flowers are much less conspicuous than the others, 
yet they produce much seed. Every one knows the ordi- 
nary flowers of the violet, but most people do not know 
that violets very generally, after the blossoming season (of 
their showy flowers) is over, produce many cleistogamous 
flowers, as shown in Fig. 135. 
