120 STRUCTURAL BOTANY 



distinct cells, each surrounding a nucleus. Thus we 

 have six cells in the embryo-sac, three at each end, 

 and also two free nuclei, which lie in the undivided 

 protoplasm which occupies all the middle part of the 

 sac (see Fig. 44, 7). The three cells at the end 

 towards the micropyle form what is called the egg- 

 apparatus (Fig. 44, 7, e.a\ Of these three, the one 

 farthest from the micropyle is the ovum (Fig. 44, 8, o). 

 The two others are termed the synergidce (s, s), because 

 they co-operate, as we shall see, in bringing about the 

 fertilisation of the ovum. The three cells at the 

 opposite end of the sac are called from their position 

 the antipodal cells (see Fig. 44, 7 and 8, an). In this 

 particular case the antipodal cells disappear before 

 fertilisation (Fig. 44, 9). Lastly, the two free nuclei 

 are called the polar nuclei (see Fig. 44, 7, p 1 and 

 /? 2 , and Fig. 44, 8, p\ because one comes from 

 each pole of the sac. Their fate is remarkable. They 

 do not remain in their original positions, but travel 

 through the protoplasm to meet each other (see Fig. 

 44, 7 and 8). When they meet they fuse together 

 into a single large nucleus, which may be called the 

 secondary nucleus of the embryo-sac (see Fig. 44, 9, 

 pp). Meanwhile the whole embryo-sac has increased 

 considerably in size, and so has the egg-apparatus, the 

 two synergidae becoming long and pointed (see Fig. 

 44, 9, s, s). 



The body of the ovule during its development 

 becomes considerably curved on itself, owing to the 

 more rapid growth of its lower side, so that the 

 micropyle ultimately comes to point almost backwards 



