292 PRIMARY CHARACTERS IN THE SPECIES OF RHEUM. 
species. I mention this that no charges of inaccuracy may be 
brought against the artist, who has really produced one of the at 
saci representations of a Potamogeton I have yet seen. 
-  EEXPLANATION = Puate 313.— Fig. 1. Upper part of barren stem. 2, 
Flowering stem. 3. Lateral branchlets 4, Part of stem with <cautread leaves. 
5. Porianth-sogment 6. Detached lower stipule with adnate leaf. 7. Section 
of peduncle. 8. Section of main stem. 
PRIMARY CHARACTERS IN THE SPECIES OF RHEUM. 
By Freperic N. Wiuams, F.L.S. 
In proposing a re-arrangement of the species of any genus with 
a ants of im improving ae a previous elassification, three thin 
nh 
organs, and in a subordinate manner have enlarged or contracted 
the scope of the genus; (8) which is more 2 ethical than botanical, 
sn far the egotistical pretensions of a writer may prompt him 
entertain ‘views’ diametrically — to what has been 
previously written upon the same subjec 
any re-arrangement of species, it is desirable to have regard 
for thie more divergent characters of the generic type which are 
emphasized in well Poepecveh pats species, and which themselves 
indicate subdivisions in which groups of species should be hora 
As long as there are hots nists who handle a genus as if it w 
‘¢ objective reality,’’ instead of treating it as an ‘ skates definition” 
invented for grouping an uncertain number of naturally allied 
species, so long will be misinterpreted the famous sentence of 
Linneus, that ‘‘ it is not the characters which make the genus, but 
the genus which makes the characters.” As new peti are dis- 
covered, and as the relative bavostahice of the individual characters 
of those already known is better understood, so will the definition 
of a genus have to be modified — _ de the new forms and 
ve certain primary characters in common. A genus is a matter 
en s 
a ter of fact. 
The fourteenth volume of DeCandolle’s Prodromus, which con- 
tais Meisner’s description of the genus Rheum, was issued in the 
and many that were at that time but little known have been more 
ren investigat ted. The continued research for the purpose of 
determining the true source of the rhubarb used in medicine has 
e main cause of the more recent investigati h 
- affinities of the different species. gations as to the 
