SEED PLANTS 171 



been found in the higher Coniferse, and it is not likely 

 that in these sperraatozoids exist. 



The development of the embryo in the Conifers shows 

 a good deal of difference in different genera. Some- 

 times but a single embryo arises from each egg-cell, as 

 in most other plants ; but sometimes, for instance in the 

 common pines and firs, each egg gives rise to a group 

 of (usually four) embryos, and the ripe seed may contain 

 more than one young sporophyte. Generally, however, 

 one of the growing embryos crowds out the others, and 

 only this one matures. As in Selaginella and the lower 

 Gymnosperms, a long suspensor (Fig. 42, J, sus) is 

 formed from the upper part of the egg, while the lower 

 portion only gives rise to the embryo itself. By the 

 rapid lengthening of the suspensor the growing embryo 

 is pushed down into the tissue of the gametophyte, 

 whose cells become gradually filled with nutrient sub- 

 stances upon which the developing embryo feeds. These 

 are not all consumed, however, but a considerable part 

 persists in the ripe seed as the " endosperm," in which 

 the young sporophyte is imbedded, and upon which it 

 draws for nourishment in the early stages of the germi- 

 nation of the seed. The young sporophyte within the 

 ripe seed already has all its primary organs developed. 

 The stem is prolonged downward into the primary root, 

 which is directed toward the opening in the integument 

 (micropyle), while the upper end of the embryo termi- 

 nates in the conical stem-apex about which is arranged 

 a circle of primary leaves, or cotyledons, ranging in 

 number from two to half a dozen or more. 



The ripe seed has a hard, usually dark-colored coat, 

 effectually protecting the delicate inner tissues; some- 



