THE LEAVES OF VASCULAR PLANTS. 305 



organs; its cellular envelope is more developed than 

 usual, and the number of stomata is greater; this is 

 observed in the young branches o^ Ephedra, Stapelia, 

 Ceropegia, Cactus, the fleshy species of JEtiphorbium, 

 XylophyUa, Casuarina, Equisetum, and in general of all 

 plants not parasitical and devoid of leaves. All these 

 branches, physiologically speaking, enjoy the function 

 of leaves, and often take their appearance and form. 

 One of the errors which must be guarded against in the 

 study of these plants, is, that the name of leaves has 

 been for a long time given to true branches ; thus, the 

 oval discs of Opuntia are compressed branches, since 

 they bear leaves, and after some years become true 

 cylindrical trunks : the true leaves of these plants are 

 the little conical or oblong bodies w^hich are situated 

 below the clusters of spiny hairs, and which fall off very 

 early. 



4th. There exist some plants, the bark of vv'hich is not 

 transformed into foliaceous surfaces, and is devoid of 

 true leaves, or has them deduced to the state of scales, 

 deprived of stomata, and incapable of physiological 

 action ; but most of these plants, and perhaps all of 

 them, are parasites; that is to say, they are endowed 

 with the faculty of implanting themselves upon plants 

 furnished with leaves, and of appropriating the sap 

 elaborated by them. 



Thus some, such as Cuscuta, attach themselves to the 

 branches of other plants, from which they absorb 

 nourishment by means of their suckers : Cassytha ap- 

 pears to live in the same manner. 



Others, such as Orobanche, grow upon the roots of 

 other plants, from which they draw an important part 

 of their nourishment : they are attached to the roots by 

 only some of their radicules, a great number of others 

 being free. These latter appear to extract from the soil 



VOL. I, X 



