96 ON VARIETIES, EACES, SUB-SPECIES, AND SPEClKS. 



(a) Persistence of the modifications of actual varieties i?i the 

 places 7vhere they have been produced. 



If MM. Sageret and Van Mons both admit that the disposi- 

 tion of plants to depart from their natural types is great in pro- 

 portion as they are already distant from those types, nevertheless 

 we think there ought to be a limit to this variation, and that this 

 limit ought to be reached sooner than the last named gentlemen 

 are disposed to allow. Be this how it may, we must not forget 

 the insufficiency of our present knowledge to fix this limit, and, 

 a fortiori, to determine whether the seeds of the individuals 

 which have attained it would themselves produce, if sown in 

 their native country, individuals identical with their parents, 

 which is M. Puvis' opinion ; or in the contrary case, to ascertain 

 the proportion of seeds which would, and those whicii would not, 

 produce their parents, and how many of those which would not 

 do so would give rise to new varieties which would themselves 

 revert to the original specific type. 



(b) Duration of varieties modified by culture. 



If our present knowledge is not sufficient to allow us to admit 

 the extinction of non-modified vegetable species under present 

 circumstances, we are not compelled to say that the varieties of 

 plants brought into existence by cultivation have an indefinitely 

 long existence, wliether we regard the life of each individual or 

 the existence of the variety itself. We imagine tliat it is per- 

 fectly possible the life of a fruit-tree may be shortened by the 

 modifications it may have undergone ; we conceive that such 

 modifications in the individuals composing the variety may 

 shorten its existence. For example, varieties with fruit so 

 modified that it produces no seed can only be propagated by 

 division, and if this ceases, the variety will become extinct with 

 the death of tliose individuals which were in existence at the 

 time that this propagation by seed stopped. 



After the preceding observations it will not be necessary to 

 criticise what M. Van Mons has said of the subject of the dura- 

 tion of our cultivated varieties and of tliose which he improved 

 by successive sowing: it will be sufficient to remark .that the 

 period of two or thi'ee centuries fixed by him for the duration of 

 the first, and the period of one-half or two-thirds of a- century for 

 that of the last, are merely fanciful. M. Puvis too, wlulst he 

 admits the principle of extinction, has vastly enlarged the term 

 of existence. In short, we admit the possibility of the extinction 

 of varieties, created by cultivation, under actual circumstances, 

 but we do not admit it for all varieties without exception and 

 when locality is not considered. This will be seen in the follow- 

 ing section (§5), where we shall consider the duration, not of 

 plants raised from seed, but of those propagated by division. 



