424 SCIENCE PROGRESS 



of the far-reaching effect of the act of fertilisation upon the 

 maternal tissues. 



Now that " double fertilisation" has been proved to occur in 

 these crosses, 1 the matter receives some measure of explanation, 

 for, whatever the view entertained as to the morphological value 

 of the tissue thus produced, there can be no doubt that the 

 characters of the hybrid endosperm referable to the race of the 

 male parent are directly transmitted by the male nucleus enter- 

 ing into its composition, and not due to some mystic influence 

 spreading through the parent, from the act of fertilisation 

 producing the embryo. In this sense at least, the endosperm 

 is a new generation whose characters are of double origin. 

 Whether we accord the title of true fertilisation to the triple 

 fusion or not, this much is certain, that we have true gametes — 

 with the reduced number of chromosomes — degraded to help in 

 the development of the victorious pair. Such a fate is not 

 without analogy in the animal kingdom, for it is said that in the 

 Sauropsida many sperms may enter the egg, one of which fuses 

 with its nucleus, while the remainder render service to the 

 fertilised egg by working up the food materials of the yolk. 

 In some of the lower animals also, supernumerary sperms which 

 have entered by chance become absorbed by the fertilised egg, 

 together with the polar bodies — potential female gametes. The 

 extra sperms have even been known to conjugate with the polar 

 bodies, a process very similar to the fusion of the second male 

 nucleus with the sister cell of the ovum in flowering plants. 

 Their development ceases, however, after a few divisions. 



I have spoken of the theory which regards the endosperm as 

 the equivalent of a once thriving embryo, debased by the intro- 

 duction of a third vegetative nucleus at the time of fertilisation ; 

 and also of the view which holds endosperm formation to be a 

 fresh start of the retarded prothallial tissues, inaugurated by 

 chance nuclear fusions. A third possibility suggests itself, 

 which has the somewhat dubious merit of partly reconciling 

 the other two, but at the same time is not entirely without 

 foundation. 



In the archegonia of all ferns, the last division which gives 

 rise to the ovum cuts off from it a nucleus known as the ventral 

 canal nucleus. This nucleus has been identified in nearly all 



1 Guignard, " La double fecondation dans le mais." Journal de Botanique, xv. 

 37-50, 1 90 1. 



