CHAP, in.] the Dogma of Constancy of Species. 137 



account of natural affinities, is due to the fact that De Candolle 

 in framing them really followed his own rules, whereas the 

 superior divisions, which are artificial, owe their existence to 

 his disregard of them. 



De Candolle declared emphatically against the old notion, 

 that the vegetable system answers to a linear series, a notion 

 which sprang from a misunderstanding of the saying, ' Natura 

 non facit saltus,' and demonstrated its impossibility by ex- 

 amples ; but he allowed himself to be too much influenced 

 by the idea which had been thrown out by Linnaeus, and taken 

 up by Giseke, Batsch, Bernardin de St. Pierre, L'Heritier, Du 

 Petit-Thouars and others, that the vegetable kingdom might 

 be compared as respects its grouping to a geographical map, 

 in which the quarters of the globe answer to the classes, the 

 kingdoms to the families, and so on. If the theory of descent 

 is to a certain degree compatible with the idea of a linear 

 sequence from the most imperfect to the highest forms of 

 plants, it is quite incompatible with the above comparison ; 

 and systematic investigation, led astray from the right path, 

 is in danger of ascribing the importance of real affinities to 

 mere resemblances of habit, incidental analogies, by which a 

 group of plants appears to be connected with five or six others. 

 In exhibiting his system on paper De Candolle allowed the 

 use of the linear sequence as a convenience, for here it was 

 not, he said, a matter of any importance, since the true task 

 of the science is to study the relations of symmetry in each 

 family and the mutual relations of families to one another; 

 yet in a linear presentation of the system for didactic purposes 

 the sequence ought not to begin with the most simple plants, 

 for these are the least known, but with the most highly de- 

 veloped. Thus De Candolle was the means of removing from 

 the system the last trace of anything which harmonised \\itli 

 an ascending and uninterrupted development of forms. Resting 

 on the doctrine of the constancy of species, and assuming that 

 every group of relationship is founded on a plan of symmetry 



