582 APPENDIX A. 



many square miles of snow, we have a like example ; as also in 

 the minute Algce, which colour the waters of stagnant pools. 

 The sudden appearance of green films on damp decaying surfaces, 

 the spread of mould over stale food, and the rapid destruction of 

 crops by mildew, afford further instances. If we ascend a step 

 to plants of appreciable size, we still find that in proportion as 

 the organization is low the fertility is great. Thus of the com- 

 mon puff-ball, which is little more than a mere aggregation of cells. 

 Fries says, " in a single individual of Reticularia maxima., I have 

 counted (calculated ?) 10,000,000 sporules." From this point 

 upwards, increase of bulk and greater complexity of structure 

 are still accompanied by diminished reproductive power ; instance 

 the Macrocystis pyrifera., a gigantic sea-weed, which sometimes 

 attains a length of 1500 feet, of which Carpenter remarks, " This 

 development of the nutritive surface takes place at the expense 

 of the fructifying apparatus, which is here quite subordinate." * 

 And when we arrive at the highly-organized exogenous trees, we 

 find that not only are they many years before beginning to bear 

 with any abundance, but that even then they produce, at the out- 

 side, but a few thousand seeds in a twelvemonth. During its 

 centuries of existence, an oak does not develop as many acorns as 

 a fungus does spores in a single night. 



Still more clearly is this truth illustrated throughout the 

 animal kingdom. Though not so great as the fertility of the 

 Protophyta, which, as Prof. Henslow says, in some cases passes 

 comprehension, the fertility of the Protozoa is yet almost beyond 

 belief. In the polygastric animalcules spontaneous fission takes 

 place so rapidly that " it has been calculated by Prof. Ehren- 

 berg that no fewer than 268 millions might be produced in a 

 month from a single Paramecium ; " f and even this astonishing 

 rate of increase is far exceeded in another species, one individual 

 of which, " only to be perceived by means of a high magnifying 

 power, is calculated to generate 170 billions in four days." | 

 Amongst the larger organisms exhibiting this lowest mode of 

 reproduction under a modified form — that of gemmation — we 

 see that, though not nearly so rapid as in the Infusoria, the rate 

 of multiplication is still extremely high. This fact is well illus- 

 trated by the polypes ; and in the apparent suddenness with 

 which whole districts are blighted by the Aphis (multiplying by 

 internal gemmation), we have a familiar instance of the startling 

 results which the parthenogenetic process can achieve. Where 

 reproduction becomes occasional instead of continuous, as it does 

 amongst higher creatures, the fertility equally bears an inverse 

 ratio to the development. " The queen ant of the African 



* PHn. ofPhys., 2nd edit., p. 77. f Ibid., 3rd edit., p 249. 



X Ibid., p. 124. 



