264 



PLANT PHYSIOLOGY AND ECOLOGY 



power of some species which produce a large number of seeds. 

 The seeds of some plants grow immediately after ripening, while 

 others grow only after a resting period of uncertain duration. 

 Even in the case of seeds from the same parent, the majority 

 germinate the first year, but some lie dormant for one or more 

 years. The period of time during which disseminules remain 

 viable is extremely diverse, though it is much longer, as a rule, 

 for seeds than for spores. The great vitality of weed seeds is 

 probably due to the vigor of the embryos. 



Fig. 106. The ecesis of young pines beneath the parent trees. 



280. The effect of habitat. The influence of the habitat upon 

 germination is often decisive. Seeds may be carried into a num- 

 ber of different formations, any one or all of which may offer 

 conditions unfavorable to germination. Habitats are of two 

 sorts with respect to the chances of germination, those that are 

 new or denuded, and those that bear plants. The probability of 

 germination is usually greater in vegetation than in denuded areas, 

 chiefly because the surface of such areas is relatively xerophytic. 

 On the other hand, the lack of competition in a denuded area 

 tends to make final establishment much more certain. 



