142 DESCRIPTIVE BOTANY. I'AHT I. 



and which practice alone can enable the systematic 

 botanist duly to appreciate. 



(135.) Xatnrnl Orders. As we make no pretensions 

 in this volume to enter upon the details of systematic 

 botany, we do not consider it advisable to present the 

 reader with a bare enumeration of the characters of the 

 natural orders which have been hitherto established in 

 the most recent works. We shall content ourselves with 

 explaining the connection which subsists, between the 

 principal groups under which Jussicu arranged the 

 natural orders, so far as they had been established in 

 his time, with the principal groups in the recent system 

 of De Candolle, under which this eminent botanist has 

 arranged the natural orders as they are at present un- 

 derstood. Jussieu threw the natural orders or families 

 with which he was acquainted, into fifteen groups, 

 which he termed classes, and these he further com- 

 bined into six principal groups or divisions ; of which 

 four belonged to Dicotyledones, and one each to Mono- 

 cotyledones and Acotyledones. De Candolle has also 

 four groups for the Dicotyledones and one for the Mo- 

 nocotyledones, but somewhat differently arranged ; and 

 he has split up the Acotyjodones into two parts, one of 

 which (although cryptogamic like the other) he classes 

 with the Monocotyledones, and retains the other only 

 as Acotyledones. He further arranges the whole of 

 vegetation under two principal heads, according as plants 

 possess, or are entirely without, any portion of a vascular 

 structure. 



