350 



Plant Physiology 



known as a perfect flower, of which the apple, cotton, 

 wheat, etc., are examples. These structures may oc- 

 cur in different flowers, termed staminate and pistillate 

 flowers, upon the same plant, that is, monoecious (one 

 household) plants, of which the corn and squash are 

 examples ; but they may occur upon different individuals, 

 that is, staminate and pistillate, or dioecious (two house- 

 holds) plants, of which latter type the hemp, certain 



FIG. 94. Carpels and stigmas (A) of orchard grass ; also enlarged view 

 of stigmatic cells and pollen germination. 



mulberries, and the date-palm are examples. In any case, 

 approximately at the time the flowers are open, or mature, 

 the anthers of healthy stamens may set free considerable 

 pollen. At about the same time the stigma or stigmatic 

 surface of the carpel is receptive; that is, generally, in a 

 condition to catch or affix pollen-grains, and to afford 

 special conditions for their germination. 



205. Pollination and pollen-tube penetration. - - Pol- 

 lination is a mechanical process. As it naturally occurs, it 



