Introduction. 5 



fishes and worms in the animal kingdom. The real resem- 

 blance of the organisms in such groups is unconsciously 

 accepted by the mind through the association of ideas, and 

 it is not till this involuntary mental act, which in itself requires 

 no effort of the understanding, is accomplished, that any neces- 

 sity is felt for obtaining a clearer idea of the phenomenon, and 

 the sense of this necessity is the first step to intentional sys- 

 tematic enquiry. The series of botanical works published in 

 Germany and the Netherlands from 1530 to 1623, from 

 Brunfels to Kaspar Bauhin, shows very plainly how this per- 

 ception of a grouping by affinity in the vegetable kingdom grew 

 more and more distinct ; but it also shows how these men 

 merely followed an instinctive feeling in the matter, and made 

 no enquiry into the cause of the relationship which they 

 perceived. 



Nevertheless a great step in advance was thus taken ; all the 

 foreign matter introduced into the description of plants by 

 medical superstition and practical considerations was seen to be 

 of secondary importance, and was indeed altogether thrown 

 aside by Kaspar Bauhin ; the fact of natural affinity, the vivify- 

 ing principle of all botanical research, came to the front in its 

 place, and awakened the desire to distinguish more exactly 

 whatever was different, and to bring together more carefully all 

 that was like in kind. Thus the idea of natural affinity in 

 plants is not a discovery of any single botanist, but is a 

 product, and to some extent an incidental product, of the 

 practice of describing plants. 



But before the exhibition of the natural affinity gave birth to 

 the first efforts at classification on the part of de l'Obel (Lobelius) 

 and afterwards of Kaspar Bauhin, the Italian botanist Cesalpino 

 (1583) had already attempted a system of the vegetable king- 

 dom on a very different plan. He was led to distribute all 

 vegetable forms into definite groups not by the fact of natural 

 affinity, which impressed itself on the minds of the botanists of 

 Germany and the Netherlands through involuntary association 



