REPRODUCTION 447 
than one may be fertilised by gametes from the same 
pollen-tube. This occurs in certain of the Cupressinex ; 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. 
