Excerpt from Structural and Systematic: The Latter Portion Being, an Analytical Key to the Wild Flowering Plants, Trees, Shrubs, Ordinary Herbs, Sedges and Grasses of the Northern and Middle United States East of the Mississippi
To this end, an analytical key, pointing out the orders of the plants apt to claim the student's attention, is prefixed to the American standard manuals of Chapman, Gray, and Wood. These contrivances may be successfully employed, though with a loss of much time, by more advanced students; but, notwithstanding their indisputable value, they will usually prove far from answering the wants of beginners. For them I have elaborated the analytical key, which makes the second part of this book. By a limited number of antitheses, it points out the very genus to which any ph?nogamous species whose name we want to know, belongs.
This contrivance is based on what is called the dichotomal method, and thus far agrees with the keys indicated above; but by pointing out directly the genera, instead of the orders, it is, of course, fitted for a comparatively rapid identification.
The dichotomal method was introduced by De la Marck, a contemporary and friend of De Candolle. He suggested and proved that he who wants to elaborate a most useful botanical key, must not take hold of some one part or organ of the vegetable exclusively, regarding its peculiar state as a sufficient, differential character of the plant, when brought contrasted to another; that he must not care whether he always associates plants, which naturally seem to be allied, or whether he contrasts them, provided this contrast helps to characterize them beyond all doubt; and, lastly, that opposite things become more evident by their juxtaposition (contraria juxta se posita magls duecscunt). This method has been adopted by many for the purpose of making intelligent young people fond of botany.
Suppose we have a dozen flowering plants before us.
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