CHAPTER XII 



THE SEED 



Changes in the Ovule. — As in the case of the parts entering into the 

 formation of the pericarp, so in that of the part forming the seed — 

 namely, the ovule — it is well to precede our study of the changes which 

 it undergoes by a consideration of the objects to be attained thereby. 



Development of the Embryo. — 

 The essential feature of the seed is 

 the possession as one of its parts 

 of a more or less rudimentary 

 plant, developed from the fertil- 

 ized oosphere, and known as the 

 Embryo, and capable of remaining 

 for a more or less extended period, 

 before germination, in a state of 

 suspended animation. 



The development of the embryo 

 commences with the division of 

 the fertilized oosphere into two 

 cells, each of which grows and 

 becomes capable of itself dividing 

 similarly. The result of such cell- 

 propagation is the production of 

 a tissue and of a body which 

 becomes elongated through suc- 

 cessive transverse divisions of its 

 cells, or certain of them, and 

 broadened by their longitudinal 



division. Several progressive forms reached by the embryo during 

 this process are shown in Figs. 365 to 368. 



Provisions Required by the Embryo. — During the period intervening 

 between the beginning and the completion of seed-formation the 

 embryo requires nourishing, and provisions for this constitutes the first 

 requirement of the process. The further development and growth of 



S66. 



Figs. 364 to 368. Figures illustrating develop- 

 ment of the embryo; the vertical chain of cells is 

 the pro-embryo, the uppermost of them becomes 

 the caulicle and the enlargement the cotyledons. 



