136 THAXSACTIOXS AND PROCEEDINGS OF THE [Sess. lxiii. 



full extent ouly after fertilisation. Though the polar 

 nuclei of the erabryo-sac do not coalesce at the actual 

 ontogenetic inception of the gametophyte, yet their fusion 

 marks the commencement of the endosperm, that is, the 

 main part, or the whole, of tlie vegetative portion- of the 

 prothallium. We see in the series commencing with the 

 Bryophyta, and culminating in the Gymnosperms, that the 

 development of the gametophyte begins with the produc- 

 tion of its vegetative parts. It is only in the higher 

 Angiosperms that the sexual cells outstrip the vegetative 

 parts (leaving the problematic antipodal cells out of count), 

 and it is likewise only in these forms that the nuclear 

 fusion occurs. It is evident that the commencement of 

 the vegetative tissue (endosperm) represents, in a pliylo- 

 genetic sense, the true inception of the gametophyte of 

 Angiosperms ; and the first sign of this inception is the 

 nuclear fusion. 



UsTiLAGiNE/E and Uredine.i^.. — The nuclear union in 

 both these families takes place at the inception of the 

 promycelium, which produces conidia. The young 

 resting spore of Entyloma is stated by Dangeard to contain 

 two nuclei, which coalesce before the spore germinates to 

 produce a promycelium with a terminal rosette of conidia. 

 In Puccinia lilv/cearum the teleutospores are arranged in 

 pairs; according to Poirault and Eaciborski (1), each young 

 teleutospore possesses two nuclei which unite before it 

 germinates to produce a promycelium with four conidia. 

 But in Coleosporium cupliraaw the teleutospore is four- 

 celled, and each of its spore-cells produces in germination, 

 not a promycelium with four conidia, but a single sterigma 

 with a conidium. We should, therefore, conclude that this 

 four-celled teleutospore, like that of Clirysopsora, represents 

 a single teleutospore which has already commenced ger- 

 mination.^ And Poirault and Eaciborski state that the 

 single mother-cell of this four-celled teleutospore contains 

 two nuclei, whicli coalesce before the transverse septa 

 appear. It is obvious that the promycelium of the Ustil- 

 agineaj and Uredineie is a relatively small and essentially 

 fructificative individual. It will, I tliink, Ije conceded 



' There seemK to be no adequate reason for adoptinj^ the view, some- 

 tiniea held, that this four-celled teleutospore represents four spores. 



