GROUP IV. PHANEROGAMIA : GYMNOSPERMJ]. 479 



the nucellus, it developes a pollen-tube which penetrates the tissue 

 of the nucellus, making its way to the archegonia which have 

 been, or are being, developed on the prothallium. inside the 

 macrospore ; the pollen-tube at length reaches the xnacrospore, 

 pierces its wall, and enters the neck of an archegoniura (when 

 scattered), or spreads out over the necks of a group of archegonia; 

 a male cell is forced out through the tip of the pollen-tube into 

 the oosphere, or into each of the oospheres of a group of arche- 

 gonia so that one male organ fertilises several archegonia (Fig. 

 302); the act of fertilisation is completed by the fusion of the 

 male pronucleus with the female pronucleus, to constitute the 

 nucleus of the oospore. 



In Welwitschia the process is somewhat different ; here fertilisa- 

 tion takes place in the tissue of the nucellus, where the pollen-tubes 

 meet and fuse with the filamentous outgrowths of the archegonia. 



The Results of Fertilisation. 



1. The fruit. In all the Gymnosperms which have a cone-like 

 macrosporangiate flower (Cycadaceae, except Cycas ; Coniferae, 

 except Taxese), one effect of fertilisation is to cause more or less 

 considerable growth in the macrosporophylls, or in the placental 

 scales, as also tissue-change resulting in their becoming woody 

 (e.g. Pinus, Abies, etc.) or fleshy (e.g. Juniperus), the product 

 being the fruit. 



The fruit-cone, in most cases, sets free the seed by the separa- 

 tion of the macrosporophylls, or of the placental scales, which fall 

 off from the axis of the cone, leaving it bare (most Cycadaceae, 

 Araucaria, Abies, Agathis, Cedrus) ; or they merely separate enough 

 to let the seeds fall out, and then the cones either remain on 

 the tree (e.g. Larix), or, as is more commonly the case, drop 

 off entire. However, where the fruit is a berry-like cone (e.g. 

 Juniperus), the macrosporophylls do not separate, and the disper- 

 sion of the seed depends on the fruit being eaten by animals. 



In other cases the effects of fertilisation extend to the bracts 

 (Ephedra) or to the perianth (Gnetum), causing them, to grow and 

 become succulent. 



2. The seed is albuminous in all Gymnosperms, the single 

 straight embryo being imbedded in the endosperm (see Fig. 300 /) 

 in all cases, also, some portion of the nucellar tissue persists as 

 perisperm, amounting, in the Cycadaceae and Coniferae, to little 

 more than a membranous layer, but in the Gnetaceae (at least 

 in Ephedra and Welwitschia) it is more considerable. 



v. S.B. II 



