CHAP. VI. FUNCTION OF REPRODUCTION. 289 



species, may be fairly stated as purely hypothetical. 

 Linnaeus supposed that only a few species or distinct 

 typical forms were originally created, and that a mul- 

 titude of others had since been derived from them by 

 repeated intermixture and crossings. He supposed the 

 species of very different genera might be capable of in- 

 termixing and producing new species, and even new- 

 genera. These speculations are wholly unsupported by 

 facts or experiments. De Candolle also supposes a de- 

 finite number of species or typical forms to have been 

 originally created, but he does not imagine any de- 

 cidedly new form or type to have ever originated from 

 them. He considers that certain hybrids can repro- 

 duce their kind, but that in such cases there exists a 

 constant tendency in the offspring to return again into 

 one or other of the original types from which they sprang. 

 Thus we should never have any strictly new type intro- 

 duced, or any form which differed very materially from 

 what was already in existence, but only a multitude of 

 minute shades of difference, in varieties which were all 

 intermediate between the original species. In this way 

 he proposes to account for the endless varieties of some 

 of our long cultivated fruits, as apples, pears, &c. The 

 subject is one of great difficulty, and it will require 

 many accurate and careful experiments to be made, 

 before we can expect to ascertain the laws by which the 

 limitation of species and the production of hybrids are 

 regulated. We are quite certain that many forms, con- 

 sidered characteristic of particular species, have con- 

 tinued unaltered in their minutest particulars for the 

 last 3000 years at least. This is proved by a careful 

 examination of the fragments of numerous plants found 

 in the catacombs of Egypt. An analogous fact is still 

 more strikingly established in the animal kingdom, and 

 for a much longer period ; since the forms of certain 

 existing species of shells have been found in those ter- 

 tiary deposits of which the geologist can say no more 

 than that they are comparatively recent in the history 

 v 



