ECOLOGY OF FLOWEKS; 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 

 gi'ow, 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. 



AVhether these ou1>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, 

 wliich bid for insect visitors or expose their pollen to be 

 blown about by the wind, are certain flowers 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 verj- generally, after the blossoming season (of 

 their showy flowers) is over, produce many cleistogamous 

 flowers, as shown in Fig. 135. 



