REPRODUCTION. 649 



drawn, that though monoecious Phanerogams are strictly 

 speaking dioecious, yet they are not so physiologically. The 

 explanation is this; that in the life-history of the Phanero- 

 gams the female oophore-generation has come to be merged 

 in the sporophore-generation, so that oosphere and pollen- 

 grain in the monoecious forms stand in the same physiological 

 relation to each other as two gametes produced by the same 

 plant, a relation which is too close to admit, in many cases, of 

 a fertile sexual process taking place between them. 



By his extended observations on the relative efficiency 

 of cross- and self-fertilisation, Darwin proves that the offspring 

 of the union of sexual reproductive cells derived from two 

 distinct individuals have an immense advantage in height, 

 weight, constitutional vigour, and fertility, over the self- 

 fertilised offspring of one of the same plants. This fact 

 affords the clue which we are seeking as to the importance 

 of the sexual process. By means of the sexual process the 

 production of more numerous and more vigorous individuals 

 by cross-fertilisation is rendered possible, and the maintenance 

 of the species ensured. 



We will now briefly refer to the fact of sexual degene- 

 ration. It is remarkable that this is characteristic of plants 

 which are either parasitic or saprophytic in habit, such as the 

 Fungi and certain Phanerogams (Balanophorese, Loranthaceae, 

 Santalaceae), but we are unable at present to give any satis- 

 factory explanation of this interesting correlation. 



We go on now to consider the relation of the offspring 

 to the parent or parents, to consider in other words, the facts 

 of Heredity. We can readily understand that an individual 

 produced by vegetative reproduction resembles its parent. 

 This is also the case with regard to an individual developed 

 from an asexually produced spore, at least in those plants 

 which have no alternation of generations. In plants which 

 have an alternation of generations, it is, as we have seen, the 

 alternate generations which resemble each other ; sporophore 

 resembles sporophore, and oophore resembles oophore. The 

 hereditary characters of the sporophore are transmitted 

 through the oophore to the succeeding sporophore ; and 



