XXVI INTRODUCTION. 



must be evident to the most careless thinker that such resemblances are 

 trifling. 



That which really determines aflSnitj is correspondence in structure. It 

 may be said that those plants are most nearly related which correspond in 

 the greatest number of points, and those the most distantly in which we 

 find the fewest points of correspondence ; and this must be true when we 

 remember that if every point in the structure of any two plants is found to be 

 alike, then those two must be identical. But it will be obvious that an 

 examination of all plants through every detail of their organisation is 

 impracticable ; it has never in fact been accomplished in any one case. 

 Experience must have shown that the organs of vegetation are of very 

 different degrees of value in determining resemblance in structure, that 

 some are of paramount importance, others of less consequence, and others 

 of comparative insignificance. Hence the relative value of characters 

 forms a most important part of the study of the Botanist ; it is in fact the 

 pivot upon which all the operations of a systematist must turn. 



The only intelligible principle by which to estimate their respective value is 

 according to their known physiological importance ; regarding those organs 

 of the highest rank which are most essential to the life of the plant itself ; 

 placing next in order those with which the plant cannot dispense if its race 

 is to be preserved ; assigning a still lower station to such organs as may be 

 absent without considerable disturbance of the ordinary functions of Hfe ; 

 and fixing at the bottom of the scale those parts, or modifications of parts, 

 which may be regarded as accessory, or quite unconnected with obviously 

 important functions. 



The first oflSce which all organised beings have to perform is that of 

 feeding ; for it is thus only that their existence is maintained. The second 

 is that of propagating, by means of which their species is perpetuated. 

 These being functions of the highest importance, it is reasonable to con- 

 clude that the organs provided for their proper execution must be of the 

 highest importance also, and hence that they are beyond all others valuable 

 for the pui-poses of classification. And, again, because the power of feeding 

 must come before that of propagating, it might be conjectured beforehand 

 that the organs destined for the former operation would afford the first elements 

 of a Natural method. But since the action of feeding is very simple in the 

 Vegetable Kingdom, because of the similar modes of life observable among 

 plants, while, on the contrary, the act of propagation is highly diversified, 

 on account of the very varied nature or structure of the parts by which it 

 is accomplished ; so might we conjecture that the organs of nutrition 

 would afford but few distinctions available for purposes of classification, 

 while those of fructification would furnish many. And such is the fact. 

 Hence it is that the great classes of plants are principally distinguished by 

 their organs of growth, and that in the numerous minor groups such pecu- 

 liarities are comparatively disregarded, their chief distinctions being derived 

 from their parts of reproduction. These principles are more fully expressed 

 in the following axioms : — 



1. Peculiarities of structm-e which are connected with the manner in 

 which a plant is developed are physiological ; those which are connected 

 with the manner in which parts are arranged are structural. Physiological 

 characters are of two kinds, viz., those which are connected with the mode 

 ^f g'i'owth {the organs of vegetation), and those which regulate reproduc- 

 tion [the organs of fructijication). Physiological characters are of greater 

 importance in regulating the natural classification of plants than structural. 



