GROWTH AND SEXUAL GENESIS. 449 



together of the opposite halves of the endochrome into a 

 ball. Mostly, however, sporangia are products of conjuga- 

 tion. The protoplasmic contents of two cells unite to form 

 the germ-mass or zygote; and these conjugating cells may be 

 either entirely independent, as in many Desmidiacece and in 

 the gametes of many Confervoidece; or they may be two of 

 the adjacent cells forming a thread, as in some Conjugates 

 and the gametes of Confervoidece; or they may be cells 

 belonging to adjacent threads, as in other Conjugates. But 

 whether it is originated by a single parent-cell, or by two 

 parent-cells, the zygote, after remaining quiescent until there 

 recur the fit conditions for growth, either breaks up into a 

 multitude of spores, each of which produces an individual 

 that usually multiplies asexually, or germinates directly to 

 produce one new individual; and the fact here to be noted 

 is, that as the entire contents of the parent-cells unite to 

 form the zygote, their individualities are lost in the germs of 

 a new generation. In these minute simple types, sexual 

 propagation just as completely sacrifices the life of the 

 parent or parents, as does that form of asexual propagation 

 in which the protoplasm resolves itself directly into zoo- 

 spores. And in the one case as in the other, this sacrifice 

 is the concomitant of a prodigious fertility. Slightly 



in advance of this, but still showing us an almost equal loss 

 of parental life in the lives of offspring, is the process seen in 

 such unicellular Algce as Botrydium, and in minute Fungi of 

 the same degree of composition. These exhibit a relatively- 

 enormous development of the spore-producing part, and an 

 almost entire absorption of the parental substance into it. 

 As evidence of the resulting powers of multiplication, we 

 have but to remember that the spread of mould over stale 

 food, the rapid destruction of crops by mildew, and other 

 kindred occurrences, are made possible by the incalculably 

 numerous spores thus generated and universally dispersed. 



Plants a degree higher in composition supply a parallel 

 series of illustrations. We have among the larger Fungi, in 

 75 



