378 



THE SPERMATOPHYTES 



the carpels to form different types of pistils are described in 

 Sees. 156 and 157. 



Another characteristic of the angiosperm is the production 

 of fruit. A fruit is a ripened ovule case, or ovary, frequently 



FIG. 302. Anther and pollen of the lily 



A, mature anther, showing the four locules, or chambers, containing pollen grains : 

 the anther opens lengthwise on both sides along the lines of cells shown at z. 

 B, stages in the formation of pollen grains in a group of four (tetrad) within 

 the pollen mother cell. C, mature pollen grain with early stages in the devel- 

 opment of the male gametophyte: t, tube nucleus; g, generative nucleus 



