SEEDS WILL NOT ALWAYS PRODUCE HEALTHY PLANTS. 475 



the contrary, the seedlings were often more prone to disease 

 than their parents. 



But although it cannot be said that species wear out or 

 degenerate, whatever their mode of propagation, it is confidently 

 asserted that varieties, themselves artificial productions, obey 

 another law, and that they do in fact perish from gradual loss 

 of vitality. Passing by the objection that nobody has yet been 

 able to show how what is called a species among plants really 

 differs from what is called a variety, a very little examruation 

 appears to negative the idea of a degeneracy of race being any 

 part of the System of the Universe. 



Some maintain that vegetable, like animal life, has its fixed 

 periods of duration, and that there is a time beyond which the 

 debility incident to old age cannot be warded off; and this is true, 

 so far as radividuals are concerned. But it is to confound indi- 

 viduals with races to infer from this that all the cultivated races 

 of plants require to be incessantly renewed by seed, in the 

 absence of which precaution they gradually become unhealthy, 

 and unfit for cultivation. It is thought that although the wild 

 Potato possesses indefinite vitality, yet that the varieties of it 

 which are brought into cultivation pass their lives circximscribed 

 within very narrow limits; and the same doctrine has been 

 held concerniag fruit-trees. 



The first person who proposed this theory was the late 

 Thomas Andrew Knight, who, in the latter part of the last 

 century, finding that the orchards of Herefordshire no longer 

 contained healthy trees of certain varieties of Apple, which 

 were said to have flourished fifty years before, and failing in 

 his attempt to restore health to such varieties by grafting, 

 assumed that old age had overtaken them, and that they were 

 incurable. Thence he extended the theory to aU other plants ; 

 aad here and there writers on vegetable physiology, rather out 

 of respect to Mr. Knight's great name than from any correct 

 examination of the facts for themselves, have blindly adopted 

 his views. But reason and evidence are alike Opposed to the 

 conclusion, which seems to have sprung out of a mistaken 

 application of the laws of animal life to that of vegetables, and 

 a desire to push analogy beyond its proper limits. 



