"DOUBLE FERTILISATION" IN PLANTS 425 



Gymnosperms, and is probably always formed. It persists in 

 many instances until after the fertilisation of the ovum, and has 

 been known to divide a few times. 1 This is very suggestive, 

 considered in connection with the fact that in some Gymno- 

 sperms both the sperm nuclei enter the same archegonium. The 

 second disappointed male nucleus has also been seen to divide. 2 

 It seems not unlikely, therefore, that under some circumstances 

 these gametes, 3 which would certainly have an attraction for one 

 another, should fuse and make an abortive attempt at embryo 

 formation, analogous to the abortive fusion of sperm and polar 

 body in animals quoted above. 



If this is granted as a possibility, it does not require a great 

 stretch of imagination to suppose that the decadent organism 

 might readily be stimulated to new vegetative growth by the 

 fusion with it of a vegetative nucleus. We should then see in 

 the endosperm of Angiosperms, not the deflection of an embryo 

 from its proper development, but rather the elevation of super- 

 numerary gametes — the female of which we may suppose to have 

 been shelved for some time — to a new but subordinate existence. 



It is just conceivable that this tissue may have arisen in some 

 such way. I have assumed that the sister cell of the ovum 

 concerned in the triple fusion may be regarded as the homologue 

 of the ventral canal cell of Gymnosperms, although this is 

 largely conjectural. The third nucleus entering into the fusion 

 is one of four nuclei arising in the base of the sac and generally 

 supposed to represent the vegetative tissue of the prothallus. 

 Although it has been suggested that it is this nucleus which 

 gives the "vegetative" turn to the development of the fusion 

 nucleus, it must be borne in mind that there is very little to 

 distinguish the early stages of endosperm formation from the 

 early divisions of the embryo in some Gymnosperms, notably in 

 the cycads, where the production and differentiation of cell 

 tissues take place late. So that I would regard the vegetative 



1 Coker, " Notes on the Gametophyte and Embryo of Podocarpus." Bot. Gaz. 

 1902. 



1 Arnoldi, " Beitrage zur Morphologie der Gymnospermen. III. Embryogenie 

 von Cephalotaxus Fortunei." Flora, 1900. — Miss Ferguson, "The Development 

 of the Egg and Fertilisation of Pinus Strobus." Annals of Botany, 1901. — Miss 

 Robertson, " Studies in the Morphology of Torreya Californica." New Phylologist, 

 1904. 



3 Blackman and also Chamberlain regard the ventral canal nucleus as a 

 potential female gamete. 



