380 



THE SPERMATOPHYTES 



gymnosperms (Sec. 3 52), they develop from a group or large region 

 of cells, and not from a single surface cell as in the sporangium 

 of the common ferns. The pollen sacs open along certain lines 

 (Fig. 302, x) or by pores, and the pollen is thus set free. The 

 pollen is carried in various ways to the stigma of the pistil, as 

 described in Chapter XXXII, and its application to this structure 



FIG. 303. Section of the ovule ease (ovary) of the lily 



Diagram of a cross section of a young ovule case, showing the three carpels c ; each 

 young ovule o has a large embryo sac mother cell e within the small nucellus 

 n, and shows the developing inner and outer integuments ii and oi 



constitutes pollination in the angiosperms. Wind, direct con- 

 tact of the anthers with the stigma, or the visits of insects are 

 means by which pollination is effected in this group of plants. 



360. The carpel and the formation of the ovule. The ovules 

 are developed as outgrowths from the surface of the carpels 

 (Fig. 303), or in some cases from regions of the stem, when this 



