VEGETABLES. 



239 



variety ought to belong. Some species, apt to vary 

 during their tender age, appear then so different, 

 that the characters of the foliation are insufficient to 

 determine and recognise the same species in young 

 and old individuals. Several others, on the contrary, 

 are so exactly uniform that the specific distinctions 

 can only be established on the fructification, which 

 is itself subject to exceptions and variations. It is 

 only by comparative observations on individuals, con* 

 sidered both when grown and growing, that we can 

 arrive at the distinction of the species that resemble 

 each other so nearly, and at the distribution of the 

 varieties to their proper species when found. 



The description of the oaks of North America has 

 hitherto been obscure for several reasons : 1st. the 

 botanists who have visited that country have only 

 given detached observations upon those trees, and 

 have not attended sufficiently to the characters of the 

 fructification : 2d. the authors who have treated on 

 those subjects after them, have often united several 

 species under the same denomination : and Sd. the 

 figures they have given of American oaks, cultivated 

 in Europe, are not always correct, because their 

 growth there, is retarded by a temperature which 

 is less favourable to them than their native land, and 

 because they there preserve longer the varieties of 

 foliage, which characterise their growing state. 



To clear up my doubts I have planted and culti- 

 vated, during my residence in America, all the spe- 

 cies which I have had opportunity to observe and 

 collect ; and after two years, I had the satisfaction 

 to recognise all the varieties which had perplexed 

 me so much when I had traversed the woods. 



