CHAPTER V 



SEEDS AND FRUITS 



Nature and Structure of Seeds 



The seed is the principal structure by which plants increase 

 in number. The chief function of a seed is to produce a plant 

 like the one that bore it. For plants to increase in number and 

 at the same time thrive well, they must spread to new areas. 

 Seeds are thus so constructed that they can separate from the 

 parent plant and be carried to regions where there is opportunity 

 for new plants to develop. Seeds, being able in a dormant state 

 to live long and endure adverse conditions, are the means by 

 which those plants living only one season are able to perpetuate 

 themselves. As to origin the seed is sometimes defined as a 

 matured ovule, that is, it is an ovule in which three things have 

 taken place: (1) the fertilized egg has developed into an embryo, 

 the miniature plant of the seed; (2) the fertilized primary endo- 

 sperm nucleus with some adjacent protoplasm has produced a 

 mass of stored food or endosperm; and (3) the outer portions of 

 the ovule have been modified into a testa or seed coat. Despite 

 a wide variation in size, shape, color, and other external features, 

 seeds possess in common an embryo, stored food, and seed coat. 

 In many cases these three parts are not separate, for the endo- 

 sperm may be absorbed by the embryo during the development 

 of the seed. This is true in the Bean, Pumpkin, and a number 

 of other families, where the seeds consequently have only two 

 distinct parts, embryo and testa. 



Each part of the seed has a distinct function to perform. The 

 embryo develops into a new plant, the reserve food nourishes the 

 young plant until roots and leaves are established, and the seed 

 coat protects the embryo and endosperm during the resting stage 

 of the seed. It is due to the embryo that seeds are valuable 

 in the production of new plants, while the stored food makes 

 many seeds valuable food for animals. 



The embryo, which is the chief structure of the seed, is the 



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