THE WHITE LILY 



185 



The tube at first creeps along among the papillae of 

 the stigma, and then grows down between the lobes and 

 penetrates the middle of the style, 

 until its growing end reaches the 

 ovary (see Fig. 81). Here it grows 

 along the surface of the placenta, and 

 at last turns aside into the micropyle 

 of an ovule. Its growth still con- 

 tinues, until it makes its way between 

 the cells of the nucellus to the em- 

 bryo-sac, which it enters, usually pene- 

 trating for a short distance between 

 the synergidae to the ovum (see Fig. 

 86). Here the growth of the tube 

 ceases. The length which it has 

 attained is enormous compared to 

 the size of the pollen-grain, for in 

 a large Lily the nearest ovule may 

 be as much as six inches from the 

 surface of the stigma. 



The large size of the pollen grains 

 and tubes has rendered it possible 

 to trace exactly what is going on 

 inside, and these changes have been 

 followed more minutely in the Lilies 

 than in any other plants. When 

 the pollen begins to germinate, the 

 vegetative nucleus belonging to the 

 large cell of the pollen-grain is the 

 first to enter the tube. It takes 

 the lead all through so long as it exists, but it 

 becomes gradually disorganised, and before the ovule 



FIG. 85. Pollen-tube 

 of a Lily on its way 

 down the style. 

 g, g, the two gen- 

 erative cells, each 

 nearly filled by its 

 large nucleus ; nv t 

 vegetative nucleus, 

 already becoming 

 disorganised. Mag- 

 nified about 450 

 diameters. (After 

 Guignard.) 



