116 On the requisites necessary 
to the discovery of that natural system upon which the great Author 
of Nature has planned the works of creation, or as regards the detec- 
tion of those laws by which the several functions of vitality are re- 
gulated. In all probability, there is ample scope for the accumu- 
lated observations of many generations yet to come, before we can 
expect that either systematic botany or vegetable physiology will 
take up their position by the side of the exact sciences. In the pre- 
sent state of our knowledge, there is perhaps most to be expected, 
towards making some decided step in advance, from those botanists 
who have it in their power to attend to the cultivation of plants in 
all its practical details. So far as any thing can be expected from 
direct observation on the structure of individual specimens, there are 
plenty of willing workmen of the most able class both at home and 
abroad, but there is a decided want of scientific experimenters, and 
until further information can be obtained from the positive results of 
experiment, we may scarcely hope to establish on a very firm basis, 
any of the more important principles of the science. Notwithstand- 
ing that every classification of plants proceeds upon the predetermi- 
nation of the specific characters of individuals,, hundreds of examples 
might be produced in proof of the real ignorance of our very first rate 
botanists, as to the limits within which a species may vary. In some 
cases they are tolerably agreed about arranging as a single species 
numerous forms possessing a marked dissimilarity ; and here they 
have been guided either by the results of experiment, or they have 
had the opportunity of seeing so many intermediate forms between 
two of the most marked varieties, as to leave no doubt that all were 
referable to a common origin. There are, however, a multitude of 
instances where the resemblance which two individuals, of somewhat 
different form, in certain respects, is decidedly striking, and which 
are nevertheless almost universally considered to belong to different 
species. There is, in short, no law whatever hitherto established, 
by which the limits of variation to a given species can be satisfac- 
torily assigned, and until some such law be discovered, we cannot 
expect precision in the details of systematic botany. In this respect 
the science is pretty much in the position which mineralogy occupied 
before the discovery of the laws of crystallography ; mineralogists 
were frequently in the dark as to what crystals were to be included 
under one species, and they knew almost nothing of the numerous 
forms in which any given species might occur, until they were ac- 
tually found to exist. But now, a single crystal at once puts the 
mineralogist in possession of the primitive form of the species, and 
he can calculate " a priori" the possible forms under which it may 
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