INTRODUCTORY ESSAY. 15 



It should not be forgotten, that the relative importance of 

 physiology is very different in the animal and vegetable king- 

 doms. In the former, structure and function operate so di- 

 rectly upon one another, that the great groups are, to a certain 

 extent, defined by well-marked external characters, which are 

 at once recognizable by the student, and are familiar, or at 

 least intelligible, to those even who have paid no attention 

 to natural history. In the vegetable kingdom this is by no 

 means the case : the processes of assimilation and secretion 

 present but little of that complication which renders the study 

 of animal physiology so important ; they are, on the contrary, 

 uniform almost throughout its whole extent, and moreover so 

 simple in their modus operandi, that this very simplicity pre- 

 vents their being rightly understood. In consequence, even 

 the two great classes of Monocotyledons and Dicotyledons are 



not distinguishable without considerable practice and study; 

 and were we dependent upon actual inspection of the organs 

 whence the essential characters of these two groups are drawn, 

 for the means of recognizing them, Systematic Botany would 

 be an impracticable study. 



Herein lies one great obstacle which meets the beginner on 

 the very threshold of his botanical studies : he sees the great 

 divisions of the animal kingdom to be recognizable by mere 

 inspection, and that familiar characters are also natural, and 

 available for purposes of classification : the very names of the 

 groups convey definite information, and to a great extent give 

 exact ideas. Birds, fishes, reptiles, etc. are all as natural as 

 they are popular divisions ; but what have we in the vegetable 

 kingdom to guide the student through the two hundred and 

 fifty natural orders of flowering-plants ? As with a new lan- 

 guage, he must begin from the very beginning, and also avail 

 himself of artificial means to procure as much superficial 

 knowledge of structure and affinity as shall enable him to see 

 that there is a way through the maze. Hence the obvious 

 necessity of an artificial system of some sort to the teginner, 

 who has, at the same time, to master a terminology, which, 



