108 ORGANOGRAPHY. BOOK I. 



anastomosisj or junction, with the back of the primary vein, 

 which hes next them. That part of the primary vein which 

 is between the junctions thus described, having a curved di- 

 rection, may be called the curved vein. Between this latter 

 and the margin, other veins, proceeding from the curved veins, 

 with the same curved direction, and of the same magnitude, 

 occasionally intervene : they may be distinguished by the name 

 of external veins {Jig. 53. 1). The margin itself and these 

 last are connected by a fine net-work of minute veins, which 

 I would distinguish by the name of marginal veinlets. From 

 the midrib are generally produced, at right angles with it, and 

 alternate with the primary veins, smaller veins ; which may 

 not improperly be named costal veins {Jig. 53. 5). The pri- 

 mary veins are themselves connected by fine veins, which 

 anastomose in the area between them. These veins, when they 

 immediately leave the primary veins, I call proper veinlets 

 {Jig. 53. 4) ; and where- they anastomose, common veinlets. 

 The area of parenchyma, lying between two or more veins or 

 veinlets, I name with the old botanists intervenium. 



These distinctions may to some appear over-refined ; but I 

 am convinced that no one can very precisely describe a leaf 

 without the use eitiier of them, or of equivalent terms yet to 

 be invented. Upon these principles leaves may be con- 

 veniently divided into the following kinds: — 



1. Veinless {avenium), wlien no veins at all are formed, 

 except a slight approach to a midrib, as in Mosses, Fuci, &c. 

 Leaves of this description exist only in the lowest tribes of 

 foliaceous plants, and must not be confounded with the fleshy 

 or thickened leaves common among the higher orders of 

 vegetation, in which the veins are by no means absent, but 

 only concealed within the substance of the parenchyma. (See 

 No. 10.) Of this De Candolle has two forms, — first, his 



Jblia nullinervia, in which there is not even a trace of a 

 midrib, as in Ulva; and second, his Jolia Jalsinervia, in which 

 a trace of a midrib is perceptible. These terms appear to me 

 unnecessary; but, if they be employed, the termination nervia 

 must be changed to venia. 



2. Equal-veined {cequalivenium)^ when the midrib is per- 

 fectly formed, and the veins are all of equal size, as in Ferns- 



