INTRODUCTION. xxv 



The true principles of classification, however much they may have been 

 amplified and refined upon, were in reality expressed by Ray, when he 

 defined a Natural System to be that which neither brings together dissimilar 

 species, nor separates those which are nearly allied. However much the 

 words of this definition may have been varied, it still retains the very 

 meaning given to it by its author. A species, said Jussieu, consists of 

 individuals very much alike in all their parts, and retaining their resem- 

 blances from generation to generation. Those species are to be associated 

 which correspond in the greater number of their characters ; but one 

 constant is of more importance than several inco7istant characters. On 

 these two axioms hangs the ivhole principle of Natural classification. — 

 (Genera Plantarum Prsef.) And then he proceeded to show how a group 

 of species combined upon this principle forms a Genus, of Genera an 

 Order, and of Orders a Class ; the same rules of combination being observed 

 throughout, with this difi'erence only, that the larger the group the fewer 

 the characters by which it is limited {Quo generalior enim extat plantarum 

 ordinatio qucelibet, eo paucioribus utitur signis definientibus). 



But it is far more easy to lay down principles than to put them in execu- 

 tion. The definition of Ray is perfect, but its application is surrounded 

 with difiSculty. The very first point to settle in attempting to carry out his 

 views is by what rule the dissimilarity or alliance of species is to be deter- 

 mined. In fact, very different ideas of likeness or unlikeness are enter- 

 tained by difi'erent observers. The common people can see no difi'erence of 

 moment between a Daphne, and a Cherry, and a Rhododendron, but call 

 them all Laurels, although a Botanist fails to perceive their resemblance. 

 On the other hand, there seems to the vulgar eye no connection between 

 the Hemp plant and the Mulberry tree, and yet the Botanist brings them 

 into close alliance. Nor are these conflicting views confined to the ignorant 

 and the uneducated ; such difierences of opinion may be found among 

 Botanists themselves. For instance, Linnaeus joined Arum with Phyto- 

 lacca under his Piperitse, and Convolvulus with Viola under his Campa- 

 nacei, combinations which modem Botanists entirely repudiate ; and in 

 like manner the association of Hugonia with Chlenads by Endlicher, of 

 Nepenthes with Birthworts by Brown, of Planes with Witch Hazels by 

 Adolphe Brongniart, of Vines with Berberries by the Author of this work, 

 of Spurgeworts with Heathworts and Chenopods by Fries, are so many 

 modem instances of peculiar views from which other Botanists withhold 

 their assent. 



It is therefore of the first importance to settle with something like 

 precision what it is that constitutes likeness among plants, or, as it is 

 technically called, their affinity. 



The reason why the vulgar commit mistakes in judging of natural 

 affinity is, because they draw their conclusions from unimportant circum- 

 stances, the chief of which are size, form, and colour. The similitude of 

 size gave rise to the old notion that all trees made a class by themselves ; 

 which is as if in a classification of animals the horse, the lion, and elephant 

 were placed in a different part of the animal kingdom from the rat, the cat, 

 and the goat. Form is another of the false guides which lead to error ; if 

 all round-leaved or square-stemmed plants are to be associated, so ought 

 glass to be classed with the diamond when it is cut to the same shape. 

 Colour is less a source of mistake, and yet it is sometimes unconsciously 

 employed by the superficial observer, as when he calls all yellow-flowered 

 Composites Marigolds, and all white-flowered vernal bushes Thorns. It 



