XXX INTRODUCTION. 



them, to render their distinctions nugatory, and by another, clear and pre- 

 cise. Now, if the supposed groups are really as closely allied, as for this 

 argument we may assume them to be, it can be of no possible importance 

 theoretically, whether a given Genus or Order is placed in the one or the 

 other. The near consanguinity of the two does away with all importance 

 in such a case. In Physical Geography it is of no consequence whether Lon- 

 don is stationed in Middlesex or Surrey ; and in like manner, in Theoretical 

 Botany, the place of a given Order may be equally indifferent. But it may 

 be of great consequence practically, because a definition of limits may be 

 possible or not, according to the arrangement. For example, let us take 

 the Solanal and Bignonial Alliances. These touch at the Orders of Night- 

 shades and Figworts respectively. If Nightshades are placed in the Bignonial 

 Alliance because of their intimate rel?ition to Figworts, no apparent means 

 remain of clearly defining what is meant by the Bignonial AlUance. If, on 

 the other hand, Figworts are stationed in the Solanal Alliance, then the 

 distinctive characters of that Alliance are also rendered obscure and diffi- 

 cult, or impossible of application. But place Nightshades in the Solanal, 

 and Figworts in the Bignonial Alliance, and the language of Botanists 

 affords as clear a discrimination as can be wished for. And so of other cases. 

 Indeed, I am so persuaded of this, that in my opinion aU instances of con- 

 fused and vague characters are only so many proofs of Botanists not having 

 clearly understood the plants that they have endeavoured to classify.* 



It will, perhaps, be alleged that the doctrine just inculcated is directly 

 opposed to the first principles of a Natural System : but such is not the case. 

 No absolute limits, in fact, exist, by which groups of plants can be circmn- 

 scribed. They pass into each other by insensible gradations, and every 

 group has apparently some species which assumes in part the structure of 

 some other group. Two countries are separated by a river whose waters 

 are common to both banks : in a geographical division of territory the river 

 may be assigned to either the left bank or the right bank, but such an 

 arrangement is arbitrary ; and yet the interior of the countries is unaffected 

 by it. So with the groups of plants ; it cannot be of any possible conse- 

 quence whether an intermediate or frontier plant be assigned to one group 

 or another, and convenience alone should be considered in such a matter. 

 This long since led me to offer the following observations, the justice of 

 which, much more experience entirely confirms : — ''All the groups into 

 which plants are thrown are in one sense artificial, inasmuch as Nature 

 recognises no such groups. Nevertheless, consisting in all cases of species 

 very closely allied in nature, they are in another sense natural. But 

 as the Classes, Sub-classes, Alliances, Natural Orders, and Genera of 

 Botanists, have no real existence in nature, it follows that they have no 

 fixed limits, and consequently that it is impossible to define them. They 

 are to be considered as nothing more than the expression of particular ten^ 

 dencies (nixus), on the part of the plants they comprehend, to assume a 

 particular mode of development. Their characters are only a declaration of 

 their prevailing tendencies." 



We must not, however, deceive ourselves with the expectation that by 

 this or any other expedient definitions in Botany will become possible. 

 Mathematical precision is unknown in such subjects, and exceptions occur 



♦ No Botanist will regard this as an offensive remark. It is the misfortune, not the fault, of men 

 of science, that they cannot investigate everything with their own eyes, and that they are compelled, from 

 the vastness of their subject, to take much of all they study upon trust. In Botany this is most especially 

 the case ; for who has ever been able to examine one-tenth of all the plants he speaks of, with minute 

 accuracy ? 



