ox VARIETIES, KACES, SUB-SPECIES, AND SPECIES. 95 



First period of Vegetable Life) ; 2. the influence of causes ca- 

 pable of acting differentTy according to the weather, or some 

 other peculiar circumstance, in one and the same place. And 

 let us also call to mind the influence of the time of sowing, which 

 may vary as well from accident as the will of man. (§ III. Se- 

 cond period of Vegetable Life.) 



Second Remark. — Van Mons, after stating that, as a condition 

 indispensable for the modification of a plant, it should be re- 

 moved from its native country, and that the variation is esta- 

 blished by the second sowing in the place to which the plant has 

 been removed, adds, that it cannot be afterwards changed from 

 the species (of the modified plant) which it continually propagates 

 from generation to generation. This we think to be incorrect. If 

 there be some species which are not, and some which are disposed 

 to be modified, there are among the latter some individuals wliicli 

 tend to assume their primitive form when exposed to circum- 

 stances similar to those which existed before any modification 

 took place ; whilst other individuals appear to preserve their mo- 

 difications out of the circumstances which caused them. Neither 

 do we admit that as a principle the modifications are invariably 

 produced at the second sowing; we are of opinion that they are 

 produced gradually, by successive generations, under certain cir- 

 cumstances, and that they cease wlien a sort of equilibrium is 

 established between the external agents and the organic forces 

 peculiar to the species. 



Surely if the modifications of seedlings were so easy and pro- 

 found in individuals of the second sowing, we could never under- 

 stand how Duhamel, the three MM. Alfroy, de Lieusaint, 

 never obtained any good result from the fruit-trees tliey raised 

 from seed ; we could not vuiderstand how M. Vilmorin, wlien 

 he sowed pips of the best pears, only obtained a small number 

 of individuals bearing good fruit, the greater part of tliem having 

 an evident tendency to revert to their wild state. It was in 

 consequence of such results that we were led to observe the ne- 

 cessity which existed of noting by numbers the proportion of 

 individuals which difi'ered from the rest, whether from the sowing 

 of cultivated or of wild plants ; in short, whenever the modifica- 

 tions of plants were made an object of study. 



The consequences which we have just drawn from the facts 

 before stated are limited to those stated: we now have to 

 examine the question of the effect of time on our varieties of 

 fruit-trees, in the places where they have been modified, under 

 the double view, 



(a) of the persistence of actual modifications ; 



(b) of the duration of the varieties presenting them con- 

 sidered as living bodies. 



