332 THE INDUCTIONS OF BIOLOGY. 



While, however, the general truth that organisms of a 

 given type uniformly descend from organisms of the same 

 type, is so well established by infinite illustrations as to have 

 assumed the character of an axiom; it is not universally 

 admitted that non-typical peculiarities are inherited. Many 

 entertain a vague belief that the law of Heredity applies 

 only to main characters of structure and not to details; 

 or, at any rate, that though it applies to such details as 

 constitute differences of species, it does not apply to smaller 

 details. The circumstance that the tendency to repetition 

 is in a slight degree qualified by the tendency to variation 

 (which, as we shall hereafter see, is but an indirect result 

 of the tendency to repetition), leads some to doubt whether 

 Heredity is unlimited. A careful weighing of the evidence, 

 however, and a due allowance for the influences by which the 

 minuter manifestations of Heredity are obscured, may remove 

 this scepticism. 



First in order of importance comes the fact that not only 

 are there uniformly transmitted from an organism to its off 

 spring, those traits of structure which distinguish the class, 

 order, genus, and species; but also those which distinguish 

 the variety. We have numerous cases, among both plants 

 and animals, where, by natural or artificial conditions, there 

 have been produced divergent modifications of the same 

 species; and abundant proof exists that the members of any 

 one sub-species habitually transmit their distinctive pecu 

 liarities to their descendants. Agriculturists and 

 gardeners can furnish unquestionable illustrations. Several 

 varieties of wheat are known, of which each reproduces itself. 

 Since the potato was introduced into England there have 

 been formed from it a number of sub-species; some of them 

 differing greatly in their forms, sizes, qualities, and periods 

 of ripening. Of peas, also, the like may be said. And the 

 case of the cabbage-tribe is often cited as showing the per 

 manent establishment of races which have diverged widely 

 from a common stock. Among fruits and ilowers the multi- 



