ORGANS OF NUTRITION. 157 



regards their form, general outline, &c., are almost infinite ; 

 hence we require a corresponding number of terms to define 

 them. These terms are also applied in a similar sense to describe 

 all the other compound organs of the plant Avhich possess a defi- 

 nite shape, as the parts of the calyx, corolla, &c. It is abso- 

 lutely necessary therefore that the student should understand 

 their application before he can make any progress in descrip- 

 tive botany. To treat of them fully here however would be 

 out of place, as this part of the subject comes properly under the 

 head of Glossology, or that department which has for its object 

 "the terms used in botany." We shall confine our attention to 

 the more important modifications. 



According to DeCandolle, the shape of leaves depends upon 

 the distribution and length of the veins, and the quantity of 

 parenchyma which is developed between them; the general out- 

 line or figure being determined by the former, and the condition 

 of the margin by the latter. These views have not however 

 been confirmed by De Merckhn, who found, in studying the 

 development of leaves, that the veins were not developed till a 

 period subsequent to that of the parenchyma, and that, more- 

 over, the form was generally established previous to their 

 formation. The outline or figure of the leaf cannot tlierefore 

 depend upon the veins. While the views of DeCandolle may 

 be thus shown to be incorrect in a scientific point of view, 

 still if that be borne in mind, it is convenient, to say the 

 least, to study the almost infinite modifications of leaves with 

 reference to his vicAvs, as it is always found that there is a 

 mutual adaptation between the venation of the leaf and its 

 general outhne. We shall describe them accordingly to some 

 extent after this manner, and in doing so we shall divide 

 our subject into five heads to be treated of as follows : — 

 1. Margin; 2. Incision; 3. Apex; 4. General Outline; 5. 

 Form. 



1. Margin — We have already stated that the condition of 

 the margin is dependent upon the extent to which the par- 



Fig. 300a. 



Fig. 300a. Diagram showing the condition of the margins of the leaves. 

 a. Bicrenate. h. Biserrate. c. Duplicato-dentate. 



enchyma is developed between the veins. Thus if the par- 

 enchyma completely fills up the interstices between them, so 

 that the margin is perfectly even, or free from every kind of in- 

 cision, the leaf is entire (figs. 296 and 300), as in the Orchis 

 tribe. When the parenchyma does not reach the margin, but 



