INTRODUCTION. xxix 



separate to the greatest distance some objects which naturally touch each 

 other ; how much more impossible must it be to follow the juxtaposition of 

 matter in treating of the solid contents of a sphere ! 



An arrangement, then, which shall be so absolutely correct an expression 

 of the plan of nature as to justify its being called the Natural System is a 

 chimera.* All that the Naturalist can do is to carry into effect the prin- 

 ciples above explained, with a greater or less amoimt of skill ; the result of 

 which will be a Natural S^'stem. 



When Linnaeus attempted to form a Natural System, he merely threw 

 together such genera as he knew into 67 groups, which he called Fragments, 

 and which were equivalent to the Natural Orders of Modern Botany. Jus- 

 sieu advanced a step further, by forming 15 Classes, under which he placed 

 100 Natural Orders. At a later period the name Class was reserved for 

 the three great divisions of Acotyledons, Monocotyledons, and Dicotyledons ; 

 and the Orders were collected into smaller groups called Sub-classes ; and 

 thus, by degrees, the necessity of forming three grades of distinctive charac - 

 ters superior to genera was recognised. But our countryman, Dr. Robert 

 Brown, whose sagacity is not the least remarkable part of his scientific 

 character, long ago pointed out the insufficiency of even this amount of sub- 

 division, and proposed the combination of Natural Orders into groups 

 intermediate between Orders and Sub-classes. The necessity of this 

 measure is now imiversally acknowledged ; attempts have been made for 

 some years, by various Botanists, to work out the problem ; and I think 

 it must be conceded that a real advance has thus been made, by the efforts 

 of various independent observers, to the accomplishment of so very desirable 

 an object. To such attempts the present work is an addition. 



The leading idea which has been kept in view in the compilation of it has 

 been this maxim of Fries : Singula sphcera (sectio) ideam quandam exponit, 

 indeque ejus character notione simplici optimk exprimitur. 1 cannot but 

 think that the true characters of all natural assemblages are extremely 

 simple ; nothing can be more certain than that their value diminishes in 

 proportion to their complexity. If two objects are not to be distinguished 

 by a few simple circumstances, they can hardly be called distinguishable at 

 all. In the highest groups or classes it is always so, (see p. 4 ;) and there 

 is no apparent reason why the same rule should not oi)tain in groups of a 

 minor rank. Nevertheless, we find that this is too often lost sight of, 

 and that long details of structure are substituted for precise words of dis- 

 tinction. 



It may be, and certainly is in some measure, true, that insuperable 

 difficulties are, in the present state of our knowledge, opposed to strict 

 definitions of Natural Orders, and a fortiori of their AlUances, &c. But 

 that is no reason why we should not endeavour to render their distinctive 

 characters as precise as the nature of the subject will permit. Vague dis- 

 tinctions, which are at once the bane and opprobrium of Natural History, are 

 so repulsive to the understanding as to deter the mass of mankind from 

 giving it their attentive study. And it is not too much to assert that 

 this vagueness arises more frequently out of the prejudices or mistiness of 

 the Naturalist's own mind than out of things themselves. It will constantly 

 happen that two groups may stand, by common consent, in the nearest con- 

 ceivable relation to each other ; it is quite possible, by one way of arranging 



* Systema illud naturse ipgius absolutam (quod mera empiria captant!) mens hiiniana capere non 

 potest ; est quoddam supra naturale cujus clavem, manibus v. ingenio humano non prensandam, summus 

 tantum tenet Naturae auctor.— i-ViV* Corpus Florarum, p. xvii. 



