Page:An introduction to physiological and systematical botany (1st edition).djvu/437

 Rh system a very large assemblage of genera incapable of being referred to any Order whatever. Nor could a learner possibly use this system as a dictionary, so as to find out any unknown plant. The characters of the Orders are necessarily, in proportion as those Orders are natural, so widely and loosely constructed, that a student has no where to fix; and in proportion as they are here and there more defined, this, or any other system, becomes artificial, and liable to the more exceptions. The way therefore to use this valuable work, so as to ascertain an unknown plant, is, after turning to the Order or Genus to which we conceive it most probably allied, to read and study the characters and observations there brought together, as well as all to which they may allude. We shall find we learn more from the doubts and queries of Jussieu than from the assertions of most other writers. We shall readily perceive whether our plant be known to him or not; and if at the same time we refer it, by its artificial characters, to the Linnæan System, we can hardly fail to ascertain, even under the most difficult circumstances, whether it be