BENTHAM ON THE SPECIES AND GENEKA OF PLANTS. 147 



it in the formation of genera, orders, or other groups, and when it is 

 that we run the risk of being led astray by the too close adherence to 

 the rules laid down. 



The most important character, in plants, will always be that which 

 in the greatest number of species (or groups of species) is the most con- 

 stantly accompanied by the greatest general resemblances among those 

 species, and differences from all others — that which collects into the 

 same group species showing the greatest general conformity in the 

 structure and economy of all their parts, and which may, therefore, be 

 supposed to be the most uniformly influenced by or acting upon the 

 specific constitution of plants. 



This question of the relative importance of characters has been fre- 

 quently discussed, especially by French botanists; and by none has 

 it been so clearly put as by the elder De Candolle, in his admirable 

 " Theorie Elementaire." He there lays it down as a rule, that the 

 value of a character is in the compound ratio of the importance of the or- 

 gan it is derived from, and of the point of view in which that organ is 

 considered. 



But, in regard to the first element, how are we to determine the 

 relative importance of organs ? De Candolle indicates two modes : a 

 priori, by the consideration of the functions they perform, or the part 

 they take in the vital phenomena ; a posteriori, by the observation of 

 the extent to which they prevail, the number of species in which they 

 exist. The former mode has been the one eagerly pursued or at- 

 tempted by the greater number of generalizing botanists ; the latter is 

 that which, after all, has practically led to the best classifications ; and 

 though characterized by De Candolle as " tres ingenieux mais peu ap- 

 plicable," is really that which he has himself followed in the best parts 

 of his systematic works. 



These two modes of argument correspond to those arguments from 

 final causes, and from observation of facts, which have divided zoologists. 

 But in plants we are much less able even than in animals to trace the 

 modifications of form and structure to any final causes. The animal 

 goes after, and selects his food ; and the whole economy of his structure 

 is modified according to the nature of that food, and where and how it 

 is to be obtained. The plant is stationary and must take what food 

 comes within its reach ; and that food, and the mode of absorbing it, is 

 very similar in all species ; nor can we discover any other final cause 

 why one set of plants, for instance, should always have alternate and 

 another opposite leaves — why in Digitalis purpurea there should be 

 on an average 1200 seeds fecundated and ripened for every two pair 

 of stamens, whilst in several Acacias there should be 10,000 stamens 

 to every head of flowers, which sets and ripens some half-dozen or a 

 dozen seeds only. And yet characters like these are, in some instances, 

 so constantly accompanied by so many general resemblances as clearly 

 to distinguish natural groups of several thousand species. 



The importance of organs, also, in another way, admits of two dis- 

 tinct qualifications, not always concurrent : physiological importance 



