268 FOEMS OF LEAVES. [BOOK i. 



plants. Such a leaf is often inaccurately called veinless. 



De Candolle calls a leaf of this nature, in which the 



veins are dispersed through a large mass of parenchyma, 



as in Mesembryanthemum, vaginervium. 

 In case it should be necessary to explain the direction that 

 the primary veins take when they diverge from the midrib, 

 this can be denoted by measuring the angle which is formed 

 by the midrib and the diverging vein, and can either be stated 

 in distinct words, or by applying the following terms : thus, 

 if the angle formed by the divergence is between 10 and 

 20, the vein may be said to be nearly parallel (subparallela) ; 

 if between 20 and 40, diverging; between 40 and 60, 

 spreading; between 60 and 80, divaricating; between 80 

 and 90, right-angled; between 90 and 120, oblique; beyond 

 120, reflexed (retroflexa.) 



With regard to the forms of leaves, this subject properly 

 enters into Glossology ; because the terms applied by Botanists 

 to differences in the outline of those organs are, in fact, appli- 

 cable to any varieties in the figure of any other flat body. 

 Nevertheless, as it is desirable that the student should know 

 upon what principles the most remarkable forms of leaves, or 

 of other divided parts, are thought to be connected with each 

 other, the observations upon the subject made by Alphonse 

 de Candolle, whose Introduction to Botany may be supposed 

 to embody the latest opinions of his father, and by De 

 Mercklin, who has studied the subject with more care and 

 acuteness than anybody, are here given in extenso. 



" Leaves," says Alphonse de Candolle, " put on a multitude 

 of forms, depending upon the manner in which they are 

 severally organised, especially with regard to their division 

 and the direction of their veins. These veins being in 

 general symmetrical on the two sides of the midrib, leaves 

 themselves are almost always of some regular figure, as, for 

 instance, oval, rounded, elliptical, &c. Their regularity, 

 however, is never mathematical ; and there are certain leaves, 

 like those of the Begonia, the two sides of which are most 

 remarkably unequal. 



" Leaves are either entire, that is, without toothings' of any 



