THE NATURE OF SEXUALITY. 899 



The product resulting from the sexual process is usually a new individual which 

 has no longer any organic connexion with the mother-plant and is not united with 

 it in growth. This is the case in the Muscineae, where the sporogonium, and in 

 Phanerogams, where the embryo, is nourished by the mother-plant, but there is no 

 actual continuity of tissue between it and the latter. The case is quite different in 

 the Ascomycetes {e. g. Lichens, Eurotium, and Erysiphe) and Floridese, in which the 

 female organ itself or certain cells connected with it are stimulated by fertilisation 

 to produce new shoots from which results a fructification containing spores ; and it is 

 only after the completion of this complicated vegetative process brought about by the 

 sexual union that the spores are set free, and produce new individuals independent 

 of the mother-plant. 



The reproductive cells of the same plant do not differ merely externally ; the 

 inability of either to originate by itself a new course of development, while the two 

 together produce an organism capable of germinating, shows that the properties of 

 the two are complementary to one another. The sexual differentiation, or difference 

 between the male and female cells, which is neutralised by the act of fertilisation, 

 has been preparing for a longer or shorter time ; the product which is the result of 

 fertilisation owes its formation to the neutralising of the sexual difference. In the 

 Conjugatae and other families where the sexual difference is extremely small or even 

 imperceptible, the preceding processes of development are also alike; the mother- 

 cells of the two kinds of reproductive cells even to the earliest stage of development 

 do not differ externally. But where the sexual difference is greater, it is fore- 

 shadowed in the preceding processes of development. Thus the mother-cell of the 

 antherozoids of (Edogontum differs in form from that of the oosphere ; and this is 

 especially seen in the development of the (Edogoniese with ' dwarf males.' In 

 Vaucheria the branches which subsequently become antheridia differ at an early 

 stage from those which form the oogonia. The sexual differentiation of the Cha- 

 raceae is inaugurated long beforehand in the great difference in the development of 

 the antheridia and carpogonia, the position of the two organs on the leaf being also 

 different. In the Muscineae and Vascular Cryptogams again preparation is made 

 for the production of the antherozoids and oospheres in different ways by the 

 formation of antheridia and archegonia. But this preparation is not confined to 

 the difference between the organs which immediately produce the reproductive 

 cells ; in many classes of plants it even goes back so far that the entire plant 

 developes as a male or as a female plant, producing only male or only female 

 reproductive organs. This occurs in some Algae, Characeae, Muscineae, and in 

 the prothallia of some Vascular Cryptogams. 



The fact is very remarkable that this preparation may be carried back in the 

 development of the individual even beyond the limit marked by the alternation of 

 generations. In the Algae, Characeae, Muscineae, Ferns, and Equisetaceae, the nature 

 of the alternation of generations is such that the sexual differentiation is developed 

 in one of the generations, while it is neutralised in the succeeding generation. In 

 these cases therefore we have a sexual and an asexual generation in the course of 

 the development of the same individual ; the asexual generation is the product 

 of the neutralising of the sexual differentiation of the sexual generation. The two 

 generations, especially in Muscineae and Vascular Cryptogams, differ essentially from 



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