CHAPTER VII 

 FRUITS, SEED, AND SEEDLINGS 



Development of the Seed. — We have seen how a male 

 nucleus of the pollen tube unites with the egg or embryo 

 (female) nucleus of the embryo sac. The fertilized egg 

 then starts upon a series of divisions, and by growth and 

 development, the young plant or embryo is formed. It 

 may be partially or totally imbedded in the endosperm. 

 In some seeds (bean), the endosperm is lacking, and the 

 embryo occupies the entire space within the seed coats. The 

 cells of the nucellus are in part absorbed by the developing 

 embryo, and at most the nucellus is represented by a very 

 thin and compressed layer just within the inner integument. 

 The integuments of the ovule become harder, less permeable, 

 and form the seed coats. The micropyle is still evident in the 

 mature seed as a small opening. 



The embryo or young plant has three main parts: (i) 

 one or two cotyledons; (2) the hypocotyl, which includes all 

 of the embryo below the cotyledons and terminates in the 

 first root or radicle; and (3) the growing point of the shoot, 

 upon which are a few leaves, making up a bud. 



The parts of a representative mature seed may be 

 summarized as follows: 



1. Seed coats. 



2. Nucellus. 



3. Endosperm. 

 [ Growing point of shoot, with leaves (bud) . 



4. Embryo { Cotyledon or cotyledons. 

 i Hypocotyl, terminating in the young root or radicle . 



57 



Seed 



