472 



deduce the order of the genera theoretically, in order to group them 

 into families, he imitated the manner in which the genera themselves 

 were formed. Botanists, struck with the complete and constant re- 

 semblance of certain individuals, had collected them into species ; 

 then, according to an equally constant resemblance, but much less 

 complete, had collected the species into genera. The characteristics, 

 which may vary in the same species, will depend on causes not innate 

 in the plant, such as its height, the hardness or softness of its wood, 

 certain modifications of shape and colour, &c, which change with 

 the soil, the climate, and other purely accidental influences. The 

 specific characteristics, on the contrary (those which ought to be 

 presented by every individual, that is connected with others in form- 

 ing a certain species, whatever may be the circumstances in which it 

 is placed), will be inherent in the very nature of the plant. Amongst 

 these characteristics there ai'e some more important than others, less 

 subject to vary in the different individuals; these, being always 

 found in a certain number of species, impress upon them a resem- 

 blance sufficiently striking to allow us to constitute a genus, 

 These will therefore have more value on account of their gene- 

 rality than the specific, and the specific than the individual. But 

 how can we appreciate these different values ? Nature herself has 

 indicated to the observer the species and several of the genera by the 

 points of resemblance with which she marks certain vegetables ; be- 

 yond these genera this conducting thread was wanting, since all 

 botanists, agreeing in almost everything up to this point, differed af- 

 ter they reached it, and followed each a separate route. There are, 

 however, several large groups of vegetables connected with one ano- 

 ther by characteristics of resemblance so evident, that they cannot 

 escape the notice of the most casual observer, much less of a botanist. 

 Besides these points of resemblance, common to every species of one 

 of these groups, there are some which are only common to a certain 

 number among them ; so that it may be subdivided into a large num- 

 ber of secondary groups. These had been recognized as genera by 

 botanists. There were, therefore, already a few collections of genera 

 evidently more similar to one another than they were to those of any 

 other group, or, in other terms, some families undeniably natural. 

 Jussieu thought that this was the key of the natural method, since, 

 by comparing the characteristics of one of these families with those 

 of the genera which compose it, he would obtain the relation of one 

 to the other ; since, by comparing several of them with one another 

 he would see what characteristics, common to all the plants of the 



