354 



A TEXTBOOK OF BOTANY [Ch. VII, 2 



in 



The development of ovaries into fruits involves often a 

 great increase in size, as notable in the gourds. Herein is 

 involved not simply an enlargement of cells already present 

 the ovary, but abundant new cell formation from the 



parenchymatous, but not spe- 

 cially meristematic, tissue, — a 

 method identical with that by 

 which the bark of trees and 

 the chlorenchyma of leaves are 

 enlarged. 



While the ovary is develop- 

 ing to the fruit, the ovule is 

 developing to the seed. The 

 coats of the ovule harden, 

 with some changes, to the seed 

 coats; the micropyle becomes 

 sealed with corky tissue; the 

 formation of the endosperm 

 tissue is completed ; and (most 

 important of all) the fertilized 

 egg cell develops into the 

 embryo plant. 



The development of the 

 embryo from the fertilized egg 

 cell may best be traced in a 

 typical case, illustrated in Fig- 

 ure 251. First the egg cell 

 divides, and then the resultant 

 cells divide, for a time in a 

 line, forming a suspensor, the 

 end cell of which, thus brought 

 well out into the embryo 

 sac, forms the new embryo. This so-called initial cell 

 divides, as shown in our figure, and divides again until 

 there is formed a multicellular globular structure. Then 

 growth becomes more active at special points, there forming 



Fig. 250. — Doubk fertilization 

 in the embryo sac of Lilium Mar- 

 tagon, generalized. 



One of the two sperm nuclei, sp\, 

 is shown in contact with the nucleus 

 of the egg cell, ov ; the other sperm 

 nucleus, sp2, is in contact with the 

 embryo sac nucleus, ek. The cells 

 si and $2, called synergidse, and the 

 three marked a, called antipodal 

 cells, represent an inheritance of 

 the thallus of lower plants. (After 

 Strasburger.) 



