DEATH RATE OF SEEDLINGS 383 



smothered and to have its light cut off by the vege- 

 tation around it 



Plants producing small seeds, on the other hand, 

 have two great advantages. The seeds can be produced 

 in far greater numbers with an equal supply of food 

 from the parent plant, and they are much more readily 

 dispersed, so that there is more chance of many of 

 them reaching comparatively distant spots where they 

 can germinate and establish themselves, and thus 

 the species has a better chance of wide distribution 

 and ultimate survival. The two most widely distributed 

 and numerous families of flowering plants, the grasses 

 (Gramineae) and the composites (Compositae), both have 

 small one-seeded fruits, and distribution is often facili- 

 tated in the latter case by the pappus (p. 370). 



Death Rate and Competition. The death rate of 

 seeds and seedlings in nature, like that of all young 

 organisms, is enormous. Besides the large number of 

 seeds which fall in places where they cannot germinate 

 and the large number that are eaten by animals, many 

 seeds which do begin to germinate are killed at an early 

 stage by finding no suitable soil in which they can root, 

 by being smothered or cut off from light by other plants, 

 or by the attacks of fungi or small insects. At a rather 

 later stage very many are eaten off by rodents or by 

 browsing animals. No seedling of a woody plant can 

 survive, for instance, in heavily pastured grassland. 

 Perennial herbaceous plants like the grasses survive 

 in such land because of their underground and surface 

 shoot systems, which possess buds that grow out as soon 

 as the upper shoots are eaten off. 



If we suppose an annual plant to produce only ten 

 seedlings a year, and all of these survive and them- 

 selves produce seed, we should have in the twelfth 



