5.34 THE REPRODUCTIVE FUNCTIONS. 



and produce a fruit of nearly the same flavour and 

 qualities : whereas trees of the same species, which 

 grow from seed, have the characters of distinct 

 individuals, and losing all the peculiarities that 

 may have distinguished the parent, revert to the 

 original type of the species to which they belong. 

 Thus from the seeds of the golden pippin, or non- 

 pareil, arise trees bearing the common crab apple, 

 which is the natural fruit of the species. By con- 

 tinued graftings, after a long period, the vitality of 

 the particular variety is gradually exhausted, and 

 the grafts no longer bear the same fruit. This has 

 already happened with regard to the two varieties 

 of apples just mentioned. For these curious facts, 

 and the theory which explains them, we are in- 

 debted to the observation and sagacity of Mr. 

 Andrew Knight.* 



The plans hitherto noticed are suited only to the 

 simplest of vegetable or animal beings ; but for the 

 continuance of the higher races in both kingdoms 

 of nature there is required a more complex proce- 

 dure. The latent germ, contained in the seed or 

 ovum, is never developed beyond a certain point, 

 unless it be vivified by the action of a peculiar 

 fluid, w^hich is the product of other organs. Thus 

 there are established two distinct classes of struc- 

 tures ; the office of the one being the formation of 

 the seed or ovum, and that of the other the pro- 

 duction of the vivifying fluid. The eflect of this 

 vivifying fluid upon the dormant germ is termed 

 Fecundation; and the germ, when fecundated, re- 

 ceives the name of Embryo. 



* See his various papers in the Philosophical Transactions. 



