144 TEXTBOOK OF BOTANY 



union of the other nine. This trough collects and holds 

 the nectar, which is produced on the inner sides of the bases 

 of the stamens. Each stamen is composed of a long, slender 

 filament and a small anther. The anther contains two 

 pollen sacs (microspore sacs) in which the pollen grains are 

 borne. 



The history of the pollen grains of the bean is much like 

 that of the pollen grains of the pine. Each of the many 

 microspores formed in the pollen sac is a young pollen grain ; 

 but the microspore germinates while still in the sac by di- 

 viding into two cells, so that when the pollen grain is shed 

 it is no longer a microspore but a young male plant, which 

 consists of a small generative cell and a large vegetative 

 cell (Fig. 86, B). The wall of the pollen grain is compara- 

 tively thick ; . its shape and color and the nature of its outer 

 surface differ in different species. When the grains are 

 ready to be shed, the sacs that 

 contain them split open length- 

 wise. 



168. The Pistil. In the cen- 

 tral part of the flower is a pistil, 

 which may be thought of as a 

 macrospore leaf that has been 

 folded over along its midrib until 

 its edges joined. As a result, the 

 lower, enlarged part of the pistil 



FIG. 87. -T bean, ovule < the ovar ^ contains a chamber 

 (macrospore sac) ; a, micropyle; within which the ovules (macro- 

 b, outer integument; c, inner spore sacs) are borne. The ovary 

 TS AflI! Hes horizontally inside the trough 

 tion by Miss Mabel Brown. formed by the nine united sta- 

 mens ; it is rather long and is 



the part which will develop later into a pod. The ovules, 

 usually not less than four nor more than ten in number, 

 are attached alternately to the two edges of the leaf. 



