338 FRUITS AND SEEDS 



Most trees spread only through the agency of seeds. 

 Pines, for example, have no other means of propagation. 

 Yet the survival of trees does not depend upon seeds to 

 the degree that the survival of annuals depends upon 

 them. In order that annuals may survive, every crop of 

 seeds must be successful, while trees, if a seed crop fails, 

 have other chances of success in later seasons. 



C. Protection of and by Seeds. — It is evident that em- 

 bryos have much need of protection. They themselves 

 are dehcate structures with sHght capacity to endure un- 

 favorable conditions. The seeds which contain them are, 

 however, as a class, the most resistant of all plant struc- 

 tures. They resist drought, cold, and heat as no other 

 plant parts do. Moisture is the thing which is most Hkely 

 to rob them of their vitahty, for moisture starts sprouting, 

 and then, unless the young plant is surrounded by condi- 

 tions favorable to its continued growth, its life is soon 

 ended. Farmers long ago learned to take particular pains 

 to keep dry those seeds which they saved for planting. 



Young seeds are protected from excessive transpiration 

 and other dangers by the pericarp, which is the hardened 

 ovary wall. Edible fruits, when young, are usually Sour, 

 bitter, or hard, and this is a means of protection for the 

 immature seeds within them. The pericarp, in some cases, 

 produces spines, such as are seen on the gooseberry, the 

 chestnut, or the prickly pear. Protection by the pericarp 

 is particularly noticeable in nuts. The hulls of walnuts 

 and hickory nuts are the enlarged and fleshy calyx of the 

 pistillate flowers, but the bony, hard part is the pericarp. 

 The kernel itself is the seed. 



Protection of the embryo by the seed is principally 



