KEPKODUCTION 447 



than one may be fertilised by gametes from the same 

 pollen-tube. This occurs in certain of the Cupressineae ; it 

 is rendered possible by a multiplication of the male gametes, 

 which takes place by ordinary processes of division exhibited 

 by them as they pass down the tube. Several embryos 

 may thus arise in the seed. Usually, however, only one 

 of these undergoes a normal development. 



In many families of the Angiosperms the second of the 

 generative nuclei has been observed to fuse with the two 

 polar nuclei or the definitive nucleus of the embryo-sac. 

 The extent to which this takes place has not yet been 

 determined and its interpretation is not at present easy. 

 Some observers hold that the fusion of the cells has nothing 

 sexual about it, but is nutritive only ; others look upon 

 the so-called endosperm which results as an abortive second 

 embryo. 



