CHAPTER XXXIII. 



SEEDS AND SEEDLINGS. 



I. Seeds. 



This chapter is for reading and reference. 



341. Parts of the seed. — The seed consists of the embryo 

 surrounded by the ripened ovule and certain secondary growths. 

 Following fertilization as the embryo is forming in the embryo 

 sac, a new growth of cells is formed also within the embryo 

 sac but surrounding the embryo. This is called the endosperm. 

 The young embryo derives some of its nutriment from the endo- 

 sperm. In some seeds the nucellus (central part of the ovule) 

 forms nutritive tissue, which may be consumed during the 

 ripening of the seed, or in some seeds a portion of it remains 

 outside of the endosperm, as perisperm. 



342. Outer parts of the seed. — While the embryo is forming 

 within the ovule and the growth of the endosperm is taking 

 place, where this is formed, other correlated changes occur in 

 the outer parts of the ovule, and often in adjacent parts of the 

 flower. These unite in making the " seed, " or the " fruit. " 

 Especially in connection with the formation of the seed a new 

 growth of the outer coat, or integument, of the ovule occurs, 

 forming the outer coat of the seed, known as the testa, while 

 the inner integument is absorbed. In some cases the inner 

 integument of the ovule also forms a new growth, making an 

 inner coat of the seed (rosacese). In still other cases neither 

 of the integuments develops into a testa, and the embryo sac 

 lies in contact with the wall of the ovary. Again an additional 



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