122 On the requisites necessary 
lyx, the fertility or sterility of the upper stamina, the relative situa- 
tion of the two lobes of the anthers, the form of the extremity of 
the style, and even the general direction of the stamina characters 
which, in the rest of the tribe, are more or less constant are re- 
markably uncertain in the present series, and seldom correspond with 
the differences of habit and inflorescence. These differences, on the 
other hand, are too vague and difficult of definition to be available 
for the purpose of generic distinctions. Whilst, therefore, I have 
endeavoured, as in other instances, to take the organs of fructifica- 
tion as the bases of generic, and the inflorescence and habit of sec- 
tional characters, I am fully aware that there are many species which 
may be nearly as well placed in either of two or more sections or 
genera ; but every day brings further proof of the impossibility of 
reducing nature to any thing like mathematical accuracy." 
To pass from the requisites necessary to secure the advance of 
scientific botany, to those which may be considered essential to the 
progress of botanical physiology, we have a wider field open, 
and to a much more numerous class of observers, than the one we 
have already discussed. This part of our subject is in its first in- 
fancy, and it is in the power of any one without much difficulty, to 
make himself master of the details necessary to place him in posses- 
sion of the leading facts hitherto ascertained, and of the nature of 
those difficulties which impede the progress of this department of 
botany, and all this may be attained without the necessity of his be- 
ing previously forced to master the details of systematic botany. It 
is here that recourse to experiment is of paramount consideration. 
Although some knowledge of vegetable anatomy may be requisite, 
much may be done in researches of this kind without any minute 
acquaintance with the details of the internal structure of plants, or 
the necessity of attaining to any great degree of skill in the use of 
the microscope. Vegetable anatomy is itself comparatively far be- 
hind that of animals, and there are many points of primary import- 
ance still under dispute. Notwithstanding the many discoveries 
which have been made by the great skill of our modern miscrosco- 
pic observers, very little is known of the comparative anatomy of 
different genera, and indeed little more of the internal structure of 
plants, generally, than the forms and appearances presented by the 
several elementary organs of which the vegetable tissues are com- 
posed. We have accurate delineations of a great variety of the 
vesicles in the cellular tissue, of the ducts and tracheae composing the 
vascular, &c., but very little information has hitherto been obtained 
as to the precise offices which these several organs are destined to 
