CHAPTER XII.— POLLINATION AND FERTILIZATION. 91 



visited by diurnal insects, while those with white or light-yellow 

 corollas are often visited by moths and other insects that fly at 

 dusk, these colors being more readily perceived in the dim light 

 than others. It is by no means true, however, that all white 

 flowers are fertilized by crepuscular insects. 



Even the stripes or lines found on corollas are significant; 

 they point to the locality in the flower where the nectar is 

 secreted, and serve the purpose of guiding the insect thither. 



The disagreeably odorous flowers are attractive to some 

 insects no less than the pleasantly odorous ones are to others. 

 The giant flower of Rafflesia, for instance, has a carrion-like odor 

 and a beefy appearance which attract swarms of carrion-flies 

 that are deceived into depositing their eggs upon it, dooming 

 their maggot progeny to starvation ; in the process, however, 

 they are likely to bring pollen from another flower and deposit 

 it on the stigma. Some flowers which are visited by night-flying 

 insects withhold their perfumes by day, but dispense them freely 

 at night, as in the case of the night-blooming Jasmine (Cestrum). 

 Some flowers, also, that are cross-fertilized by day-flying insects, 

 close at night, doubtless, in some instances at least, to prevent 

 the wastage of nectar and pollen by insects that could not be of 

 service to the plant. 



We may briefly summarize, as follows, the different means 

 bv which self-fertilization is prevented among entomophilous 

 plants. 



( 1 ) By the separation of the flowers into staminate and pistil- 

 late forms, that is, by diclinism. Diclinous plants are of two kinds : 

 mona'cious, as the Begonia, where both kinds of flowers occur on 

 the same plant, and dixcious, as most Willows, where the male 

 and female flowers occur on different plants. 



(2) By dichogamy, or the maturing of the male and female 

 organs at different periods. This, occurring in flowers which 

 possess both stamens and pistils, is the same in its effects as 

 though the male and female organs were in separate flowers. 

 There are two kinds of dichogamy, one in which the stamens 

 first mature and then afterward the pistils, and the other in which 

 this order is reversed and the pistils are the first to mature. 

 Flowers of the former kind are called proterandrous, or protan- 

 drous, while those of the latter are called proterogynous or proto- 



