190 PRINCIPLES OF BOTANY, &c. 
give plants a very different appearance, as in the 
carrot, (Daucus carota). In its wild state this plant 
has no large or yellow roots; it receives these solely 
from culture. But the above rule is applicable 
solely to wild plants; however, if we can avoid 
drawing the specific character from the root, and 
can take it from other marks, it is so much the bet- 
ter, as we have not always an opportunity of exam- 
ining the root, particularly in a hortus siccus. 
§ 185. 
The stem affords a certain and obvious sponse dis- 
iinction. 
The stem seldom varies, and therefore gives an 
excellent character ; in particular the round, the cor- 
nered, the jointed, the creeping, &c. stems, are 
very steady. The branched stem is not so sure a 
mark; it is very subject to variation, and therefore 
cives no certain character. 
§ 186. 
The duration of a plant is a proper distinguishing 
mark of the species only in its native situation. 
When allied or very similar plants differ in dura- 
tion, so that one ts an annual, the other a shrubby 
plant, or even tree, they must be considered as dif- 
ferent species. But the duration of these, in the 
places where they grow wildy; must be mvesti- 
gated. All plants that are biennial with us are an- 
nual in warmer climates. Some that are perennial 
im warm countries turn annual with us: the root is 
killed 
