440 LAWS OF MULTIPLICATION. 



presently set free by the bursting of the parent-cell, severally 

 grow and quickly repeat the process. The like occurs among 

 sundry of those kindred forms of minute A Igce which, by 

 their enormous numbers, sometimes suddenly change pools to 

 an opaque green. So, too, the Desmidiacece often multiply so 

 greatly as to colour the water; and among the Diatomacece 

 the rate of genesis by self-division, " is something really ex- 

 traordinary. So soon as a frustule is divided into two, each 

 of the latter at once proceeds with the act of self-division ; so 

 that, to use Professor Smith's approximative calculation of 

 the possible rapidity of multiplication, supposing the process 

 to occupy, in any single instance, twenty-four hours, * we 

 should have, as the progeny of a single frustule, the amazing 

 number of one thousand millions in a single month.' " In 

 these cases the multiplication is so carried on that the parent 

 is lost in the offspring the old individuality disappears either 

 in the swarms of zoospores it dissolves into, or in the two 

 or four new individualities simultaneously produced by fis- 

 sion. Vegetal aggregates of the first order, have, how- 

 ever, a form of agamogenesis in which the parent individual- 

 ity is not lost : the young cells arise from the old cells by ex- 

 ternal gemmation. This process, too, repeated as it is at 

 short intervals, results in immense fertility. The Yeast- 

 fungus, which in a few hours thus propagates itself through- 

 out a large vat of wort, offers a familiar example. 



In certain compound forms that must be classed as plants 

 of the second order of aggregation, though very minute ones, 

 self-division similarly increases the numbers at high rates. 

 The Sarcina ventriculi, a parasitic plant which infests the 

 stomach and swarms afresh as fast as previous swarms are 

 vomited, shows us a spontaneous fission of clusters of cells. 

 An allied mode of increase occurs in Gonium pectorale: each 

 cell of the cluster resolving itself into a secondary cluster, 

 and the secondary clusters then separating. " Supposing, 

 which is very probable, that a young Gonium after twenty- 

 four hours is capable of development by fission, it follows 



