196 PRINCIPLES OF BOTANY, ETC. 
nitude, colour, &c. are not to be made use of, be- 
cause these things can only be understood by com- 
parison with other plants, and we have not always 
at hand the object of comparison. ‘The following, 
which errs against this rule, may serve as an ex- 
ample. 
Solanum arborescens, tomentosum, latifolium ; 
fructu magno cinereo. Barr. aequin. 104. 
Who can know from this character what plant is 
meant ? | | | 
“There must be no negative expression in the specific 
name. | 
When in a specific name it is only said what the 
plant has not, it is evident that nothing certain can 
be learned from it, e. g. 
Cuscuta caule parasitico, volubili, lupuliform1, 
aspero punctato, floribus racemosis, non conglo- 
meratis aut pedunculatis. Krock Siles. 251. 
When a genus consists but of one species, there 1s no 
occasion for a specific difference. : 
It is evident that a single species, that cannot be 
compared with another, can have no discriminating 
character. ‘Thus it is, in particular, with Butomus, 
Paris, Parnassia, &c. 
But when only one species of a genus is dis- 
covered, an accurate description must be made of 
it, that it may be distinguished if others should be 
discovered. 
§ 197. 
The complete description of the natural charac- 
ters, (§ 148), of a genus, must be made in the fol- 
lowing 
