142 



FERTILIZATION AND POLLINATION 



protected by being securely covered with a paper bag. (Fig. 

 239.) In monoecious plants, if the staminate flowers are 

 removed or covered close-fertilization is prevented. 



REVIEW. What is fertilization? Pollination? 

 Pollen germination? What is a receptive stigma? 

 How is pollen discharged? How is cross-pollina- 

 tion secured? Are plants benefited by cross-pol- 

 lination? What is meant by impotent pollen? 

 What do you understand by dichogamy? Its office? 

 Is it frequent? What is the character of insect- 

 pollinated flowers? Why is the bee an effective 

 insect in distributing pollen? What is the sig- 

 nificance of irregularity in flowers? Where is the 

 nectar borne? What are monoecious and dioecious 

 flowers? Cleistogamous flowers? Why may flowers 

 be hand-pollinated? 



NOTE. The means by which cross-pollination 

 is insured are absorbing subjects of study. It is 

 easy to give so much time and emphasis to the 

 subject, however, that an inexperienced observer 

 comes to feel that perfect mechanical adaptation 

 of means to end is universal in plants, whereas 

 it is not. One is likely to lose or to overlook the 

 sense of proportions and to form wrong judgments. 



In studying cross-pollination, one is likely to look first for devices 

 that prohibit the stigma from receiving pollen from its own flower, but 

 the better endeavor is to determine whether there is any means to insure 

 the application of foreign pollen; for the stigma may receive both but 

 utilize only the foreign pollen. Bear in mind that irregular and odd 

 forms in flowers, strong perfume, bright colors, nectar, suggest insect 

 visitors; that inconspicuous flowers with large, protruding stigmas 

 and much dry powdery pollen suggest wind-transfer; that regular and 

 simple flowers depend largely on dichogamy, whether wind- or insect- 

 pollinated. Most flowers are dichogamous. 



239. A bag covering a 

 pollinated flower. 



