CHAP. II. LEAVES. 1 1 I 



radiating leaf that the curve-veined bears to tlie straight- 

 veined; it is i\\e folium jjemiinervium of De Candolle. 



10. Hidden-veined {introvenium) . To this I i"efer all leaves 

 the veins of which are hidden from view by the parenchyma 

 being in excess, as in Hoya, and many other 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. 



It may be necessary to explain the direction that the 

 primary veins take when the}' 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 follow^ing terms thus : — if 

 the angle formed by the divergence is between 10° and 20 , 

 the vein may be said to be nearly parallel {suhparallela) ; if 

 between 20° and 40°, diveryiny ; between 40° and 60°, spread- 

 ing ; between 60° and 80°, divaricatiny ; between 80° and 90°, 

 riyht-anyled ; between 90° and 120°, oblique; beyond 120°, 

 rejlexed {^retrqflexa). 



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, ap- 

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

 Nevertheless, as it may be a matter of convenience to the 

 student to know upon what principles the most remarkable 

 forms of leaves, or of other divided parts, are thought to be 

 connected with each other, I here translate the observations 

 upon the subject made by Alphonse de Candolle, whose recent 

 Introduction to Botany may be supposed to embody the latest 

 opinions of his father. 



" Leaves put on a multitude of forms, depending upon the 

 manner in which they are severally organized, 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 alwa3's of some 

 regular figure, as, for instance, oval, rounded, elliptical, &c. 

 Their regularity, however, is never mathematical ; and there 



