REPRODUCTION AND DEVELOPMENT OF PLANTS 277 



number of fine yellow grains, called pollen. The rather stout 

 basal part of the pistil, called the ovary, contains small white 

 rounded bodies, called ovules. The beans are fastened at 

 the sides of the ovary; some seeds are fastened at the mid- 

 dle. The bean pod shows the place of attachment very 

 plainly. (LABORATORY MANUAL, Exercise XXIX.) 



313. Pollination. The pollen from the stamens is trans- 

 ferred to the tip of the pistil by some agency, such as gravity, 

 insects, birds, or wind. This process is termed pollination. 

 Small birds searching 

 for insects, and insects 

 looking for food, thrust 

 their heads or even their 

 entire bodies into a 

 flower and rub the pol- 



Anther 

 Filament 



Stigma 



Petal 



FIG. 144. FLOWER 



1. The ovary of this flower contains 

 only one ovule. How is it kept in place? 

 2. How can you tell whether this is a cherry 



len from the stamens 

 upon their bodies. As 

 they withdraw, they 

 sometimes leave some 

 pollen upon the stigma, ? r an a P ple bl ssom ? 3 fl what 9 



^ r inside the anthers of a flower? 4. What 



which is the top of the is the most common color in anthers? 



pistil; but more often 5 - w , hat r f ason can ^ g ive for the 



pistil s position in a flower? 



they carry it to the next 



flower and, entering, scatter it upon the stigma, thus securing 



pollination for that flower. . 



314. Fertilization. Microscopic study of an ovule shows 

 it to be composed of cells, one of which is called the egg cell. 

 The pollen grain contains a special cell called the sperm cell. 

 When a pollen grain is left on the tip of the pistil, a long 

 delicate tube grows from the pollen grain down through the 

 pistil till it comes to an ovule. It pierces the ovule and thus 

 reaches the egg cell. Through this tube the sperm cell of 

 the pollen grain travels, till it reaches the end of the tube 

 and meets the egg cell. The two cells, coming together, 

 unite and form a single cell. This union of egg cell and sperm 



