THE SEED 355 



and only brief reference will be made to these features, which 

 are treated there in detail and should follow this account if they 

 have not already been studied. 



341. The seed. The importance of the seed in the develop- 

 ment of plant and also of animal life can hardly be exaggerated. 

 For the plant it furnishes one of the surest means of reproduc- 

 tion not only because of protective structures, means of dispersal, 

 long vitality, etc. (see Chapter xxxin), but also because the 

 embryo plant is carried so far forward in its development that 

 it is able to take root and establish itself at once. And fur- 

 ther to aid the embryo, the seed is a storage organ of the most 

 condensed forms of food material found in plants. In this 

 respect, also, the seed has proved a most important influence in 

 shaping the habits and in a large measure the evolution of some 

 forms of animal life ; for the highest groups of animals live to 

 a very great extent directly or indirectly upon food stored in 

 seeds and certain fruits, finding there some of the richest and 

 most nutritious proteid and carbohydrate foods. The animal 

 life of the Carboniferous Age (coal age) and the periods imme- 

 diately following comprised animals of great bulk of body, but of 

 low nervous organization. They browsed on the vegetation like 

 the hay and grass-eating animals (herbivora) of to-day, and like 

 them their bodily structure and nervous system were adapted 

 to such life habits. But, later, groups arose with digestive organs 

 adapted to richer foods, and this diet became associated with 

 varied life habits, which led ,to much higher types of nervous 

 organization and bodily structure. 



342. The morphology of the seed. The morphology of the 

 seed can only be understood when the spermatophytes are 

 studied in relation to the pteridophytes. The seed plant is a 

 heterosporous sporophyte. The pollen grain is a microspore. 

 The megaspores of the seed plant are never shed. They are 

 retained in the megasporangium and never even lie freely as 

 independent cells, but are always in close physiological relation 

 to the tissue of the megasporangium. The cell which is the 



