CHAP, in.] the Dogma of Constancy of Species. 121 



though as it happens this misconception does not cause any 

 great disturbance. How inexact was his investigation of the 

 organs of fructification, when they were somewhat small and 

 obscure, is best shown by the fact that the Naiades, which are 

 made to include Hippuris, Chara, and Callitriche, appear among 

 the Acotyledons, and that Lemna and the Cycads are placed 

 with the Ferns. 



Jussieu explained the dictum, ' Natura non facit saltus,' to 

 mean that the whole body of plants in its natural arrangement 

 must exhibit a lineal series ascending from the most imperfect 

 to the highest forms ; but he does not say whether Linnaeus' 

 comparison of the natural system to a geographical map, the 

 countries in which answer to orders and classes, is also admis- 

 sible. 



His theoretical observations on the value to be given to 

 certain marks in a systematic point of view are not attractive, 

 and for the most part not very correct ; he speaks as though 

 some marks must have a more extensive, others a less exten- 

 sive value ; the perception of the fact, so far as it is true, rests 

 entirely upon induction ; that is, after the natural affinities have 

 been already recognised to a certain extent, it becomes appa- 

 rent that certain marks remain constant in larger or smaller 

 groups ; the systematist can now go on to try whether such 

 constant marks occur in other plants also, which he had 

 hitherto assigned to other groups, and thus put it to the test 

 whether those marks may not be accompanied by others, which 

 would serve to establish the affinities ; that Jussieu did so pro- 

 ceed in defining his families admits of no doubt, but he was 

 not himself thoroughly conscious of the fact ; at all events, he 

 did not extend this mode of proceeding, the seeking after 

 leading marks, to the establishing of larger groups or classes, 

 for these he founded on predetermined principles. 



Jussieu's labours as a systematist were not confined to the 

 publication of his ' Genera Plantarum ' ; on the contrary, his 

 most fruitful researches began after 1802, and were continued 



