REPRODUCTION. 417 



retain less of the peculiar characters of the individual from 

 which they spring, than those of the latter. This is re- 

 markably exemplified in the case of orchard trees, such as 

 apples and pears; for all the trees which derive their origin 

 from shoots, or grafts from the same individual, partake of 

 the same properties, and produce a fruit of 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 paculiarities 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 

 nonpareil, arise trees bearing the common crab apple, which 

 is the natural fruit of the species. By continued graftings, 

 after a long period, the vitality of the particular variety is 

 gradually exhausted, and the grafts no longer bear 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 indebted to the obser- 

 vation 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 procedure. 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, which 

 is the product of other organs. Thus, there are established 

 two distinct classes of structures; the office of the one being 

 the formation of the seed or ovum, and that of the other the 

 production of the vivifying fluid. The effect of this vivi- 

 fying fluid upon the dormant germ is termed Fecunda- 

 tion', and the germ, when fecundated, receives the name of 

 Embryo. 



The modes in which the fecundation of the germ is ac- 

 complished are exceedingly various in different classes of 

 organized beings. In all Phanerogamous plants, (so named 



* See his various pap ere in the Philosophical Transactions. 

 VOL. II. 53 



