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CHAPTER II. 
OF DESCRIPTIONS. 
We have seen that the principal characters of a plant can 
be comprehended in the essential and differential charac- 
ters. But, as these contain only such peculiarities as are 
supposed to be most essential, a great number of circumstances 
are omitted from them which, in the view of the botanist 
drawing them up, may appear unessential, but which to 
another may seem of the first importance. On this account, 
a plant cannot be considered completely known until a full 
description of every part shall have been obtained. In this 
description every circumstance connected with the external or 
internal organisation should be included, and a full state- 
ment made of all the peculiarities of every part, however 
obscure or difficult to observe. It is upon descriptions 
ot this kind that systematic botany is based. Essential and 
differential characters are only relative to the degree of know- 
ledge of the person who prepares them : a description is in- 
dependent of all relative knowledge ; it exhibits a plant as it 
actually is, without reference to its resemblances or differences. 
The former are adapted to the state of knowledge of a parti- 
cular era ; the latter, if complete, to that of all eras. 
Notwithstanding their importance, descriptions of this kind 
are very rare : they occupy too much space in books to be 
inserted conveniently ; they are difficult to draw up ; and it 
seldom happens that an observer has the means of describing 
every part of a plant : the root, or the fruit, or the flower, or 
some other part, is probably not to be procured; and this 
renders a description, even in the best hands, necessarily 
imperfect. 
In drawing up a description, care must be taken that every 
term is used in its strict sense ; that all is perspicuous and free 
from ambiguity ; and that the different parts are described in 
