804 PHENOMENA OF SEXUAL REPRODUCTION. 



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

 it in growth. This is the case even in the Muscinese, 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. Peziza, Eurotium, and Erysiphe) and Floridese, in which the 

 female organ itself or certain cells connected with it are stimulated by the act of 

 impregnation to produce new shoots from which results a sporangium containing 

 spores ; and it is only after the completion of this complicated vegetative process 

 brought about by the sexual union that the asexual 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 

 Conjugatse 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 

 spermatozoids of the (Edogonium differs in form from that of the oosphere ; and 

 this is especially seen in the development of the O^dogoniese with ' dwarf males.' In 

 Vaucheria the branches which subsequently become antheridia differ at an early 

 stage from those which produce the oogonium. The sexual differentiation of the 

 Characeae is inaugurated long beforehand in the great difference in the development 

 of the globules and nucules, 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. In Phanerogams the pollen-cells and the 

 embryonic vesicles are also produced in different structures, the anthers and ovules, 

 the difference between these organs commencing long before the formation of the 

 reproductive cells. 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 prothallia of Vascular Cryptogams ; in 

 Phanerogams the flower is sometimes exclusively male or female (monoecious 

 plants), or the same plant produces nothing but male or nothing but female flowers 

 (dioecious plants). 



This carrying back of the sexual difference to processes of development long 

 anterior in time shows how great must be the internal differentiation that finally 

 subsists between the properties of the male and female cells. 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 



