36 The New York State College of Forestry 



Pollination versus fertilization 



The higher plants, like the higher animals, exhibit sexuality 

 which insures the continuance of a vigorous race. Early sys- 

 tematists believed the stamens and pistils of flowers to be male 

 and female organs, but modern science has dissipated this belief. 

 Stamens and ovules are rather the "bearers of sexual elements." 

 The pollen grains which are loosed in immense numbers from 

 the anther sacs of the stamens bear nuclei which have within 

 them the inherent feature of the male strain, while in the interior 

 of the ovule, other nuclei are borne which are female nuclei. The 

 transfer of pollen from the stamens to the vicinity of the ovules 

 (stigma of angiosperms) is known as pollination and is brought 

 about by various agents such as wind, insects, birds, and water. 

 Subsequently the pollen grains germinate and form a tube which 

 eventually permits of the union of the sex nuclei. Between po- 

 lination and fertilization only a few hours may intervene while 

 in other cases it may be months before fertilization is assured. 



Cross pollination, that is, the transference of pollen from one 

 flower to the vicinity of the ovules of another, is desirable, and 

 nature has devised many floral modifications to bring this about. 

 Many plants exhibit diclinism, that is, imperfect flowers which 

 may be monoecious, dioecious, or polygamous, and rely on wind 

 or insects for pollination. Wind pollinated plants are usually 

 characterized by abundant pollen which is often shed in advance 

 of the leaves, inconspicuous flowers, expanded or feathery stigmas, 

 or explosive mechanisms in the stamens which catapult the pollen. 

 Flowers which are insect pollinated are usually bright colored 

 or possess nectarglands which excrete saccharine or mal-odorous 

 substances attractive to insects. 



Other plants, (some of the maples) exhibit dichogamy and 

 dimorphism as a device to insure cross pollination. In dichogam- 

 cus forms the stamens of a flower reach maturity in advance of 

 the pistil (proterandrous) or vice versa (proterpgynous) and this 

 insures the union of sexual nuclei from different flowers. 

 Dimorphic flowers are insect pollinated and have the essential 

 organs arranged differently and in such a manner that an insect 

 en visiting the one flower is dusted with pollen which is rubbed 

 off' by the stigma of the next. 



Variation in the flower. 



In addition to the floral modifications which have been obvi- 

 ously devised to insure cross pollination, flowers exhibit a truly 

 wonderful variation in form, size, and in the arrangement, sup- 



