36 On the Tinctorial Properties of 



of interrooati 112 nature; it is tlic examination of afHmtie&, 

 or the study ornatural families; for observation has taught, 

 that, in oreneral, plants \\hieh have an external rcscuibhuiee 

 in their organizaiion, retain it in the innncdiate pnneiples 

 of which they are composed. The natural classitiealion, 

 therefore, mav cive reason for eonjeeturing the virtues of 

 a new plant, bul, unfortunately, the labour which could 

 give Us any certainty in this respect has not been carried 

 to a sufficient length : — to bring it to perfection would re- 

 quire the complete union of a thorough knowledge of bo- 

 tany and chemistiT. Hitherto, therefore, the senses of 

 taste and smell have been almost the only guides for disco- 

 Veriuii in several families, exceedingly natural, one common 

 principle. In the umbelliferous plants, for example, it is 

 traced from plants the most wholesome and the most com- 

 monly used for food, such as the carrot, to those which are 

 aromatic, as fennel, and even to poisonous plants, such as 

 hemlock ; one observes in all these plants a particular taste, 

 more or less striking, and which is found in its highest 

 degree in those species accounted poisonous. It even ap- 

 pears that the observation (jf it is sometimes more certam 

 than the common classilioations. It is thus that the lagfic/a 

 could not by these means be separated from the uuibelli- 

 ferous plants, when bv ifs fruit it was referred to them only 

 with doubtfulness : v e must therefore hope that botanists 

 will be able to discover a substance common to all these 

 plants, an umbelliferous principle. In a word, there exists 

 one equally striking in the leguminous plants, from which 

 it passes also, but more rarclv, from those tliat are fit to bv 

 eaten to those which are poisonous, when it exists in ils stale 

 of irrcatesl concentration. 



But there are several other families which seem to be 

 equallv natural, and in which it is difficult to discover a 

 con)mon principle: of this kind are the rubiaeeous plants of 

 Jussieu. The signal services derived from a small number 

 of the plants which they conjprehend arc of a nature so 

 ditlerent that it i> difficult to deduce a general induction for 

 the rest. Of this kind is madder, the root of which possesses 

 a dveiny: tjuality in so eminent a degree ; coffiee, the berries 

 of which are so useful ; and, in the last place, cinchona, ren- 

 dtred so valuable bv the febriJuge qualities of its bark. 

 Though all the plants comprehended in this family have a 

 greater affinity to each other than ihey have to any other 

 of the vegetable kingdom, it'^j^^pcars itself to be composed 

 of particular groupes or species of sub-families, and eacji of 

 the plants I havt^tnentioiicd- may be considered as the type 



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