186 



STRUCTURAL BOTANY 



P.T. 



is reached is altogether lost in the protoplasm. The 

 small generative cell follows the vegetative nucleus 

 into the tube and immediately divides, so that there 

 are now two such cells, one behind the other, each with a 



large elongated nucleus 

 (see Fig. 85). When the 

 embryo-sac is reached, 

 the nuclei of both 

 generative cells, accom- 

 ON4 panied by part of their 

 protoplasm, pass out 

 through the yielding 

 membrane at the end 

 of the tube, assuming a 

 curved, vermiform shape. 

 One of the male nuclei 

 ~P2. usually the second to 

 leave the tube enters 

 the ovum, and reaches 

 its nucleus. The two 

 nuclei male and female 



FIG 86. -Upper part of embryo-sac then apply them- 



of a Lily, showing double fertil- nrtl i i * 



isation. jit, end of pollen-tube; Selves closel y together, 



s, s y the two synergidse; g.n.\ one and probably some of 



of the vermiform generative nuclei the protoplasm from the 

 from the pollen-tube in contact with 



the nucleus of the ovum, o.n.; g.n., generative cell also 



the other generative nucleus from Unites with that of the 



the pollen-tube in contact with the O vum. Fertilisation is 



two polar nuclei, p, and # 9 . Mag- v r j /T ^,. 



nified^about 400. (After Guignard!) n W accomplished (F]g. 



86, g.n, 1 , o.n.), and the 

 ovum next acquires a cell-wall of its own. 



In the meantime, as recent researches have shown, 

 a second act of fertilisation has taken place within the 

 embryo-sac. That generative nucleus which first escapes 

 from the pollen-tube passes down through the proto- 

 plasm of the sac; it increases in size, and its long, 

 worm-like form is very characteristic. It then attaches 



