1 84 



GROWTH AND WORK OF PLANTS 



In 



opening at the apex of the ovule, so that there is a communication 



from the outside. This opening is the micropyle. The stalk of 



the ovule attaches it to 

 the wall of the ovary. 

 a straight ovule the 

 stands out straight in line 

 with its stalk. In a right- 

 angled ovule the stalk 

 is bent over at the upper 

 end, so that the ovule 

 stands about at right 

 angles. In the inverted 

 ovule the upper end of 

 the stalk is bent so strongly 

 that the ovule is inverted 

 and the stalk is then fused 

 with the side of the ovule. 

 This part of the stalk is 

 called the raphe (see fig. 

 143 for details). 



302. The embryo sac 

 and egg. At the close 

 of the development of 

 the ovule a sac is formed 

 within it, known as the 

 embryo sac. This em- 

 bryo sac contains sev- 

 eral nuclei, usually eight, 

 lying in the protoplasm. 

 One of these eight nu- 



clei in the embryo sac, with the protoplasm around it, is the 



egg cell. 



303. Fertilization. When the pollen tube grows into the 



ovule at the micropyle it enters the embryo sac, into which it 



empties the two sperm nuclei. One of these s.perm nuclei fuses 



with the egg nucleus. This is fertilization. 



Fig. 144. 



iry and 



of fertilization in angiosperm. /, funicle of ovule; n, 

 nucellus; m, micropyle; b, antipodal cells of embryo 

 sac; e, endosperm nucleus; k, egg cell and synergids; 

 ai, outer integument of ovule; , inner integument. 

 The track of the pollen tube is shown down through 

 the style, walls of the ovary to the micropylar end of 

 the embryo sac. 



