628 SCALE-LEAVES, FOLIAGE-LEAVES, FLORAL-LEAVES. 



deeply into the green surface of the blade, the expressions lobed, cut, divided, or 

 partite may be used. A partite leaf appears as if composed of several leaflets, 

 and such leaves have also been termed compound leaves, especially when the 

 already-described pulvini are present at the base of the individual leaflets. 



The distribution of the strands traversinjx the trreeu tissue is connected in 

 the closest manner with the structure and shape of the leaf-blade. Expressions 

 have been borrowed from the anatomy of the animal body to designate these 

 strands, and they are called indifferently veins, ribs, and nerves. The 

 term " vein " has some justification, since most of these strands contain 

 cells and vessels which serve to conduct fluid materials to and fro ; but since 

 there are also strands which have notliing to do with this conduction, which are 

 developed exclusively for the support of the whole blade, the name is unsuit- 

 able, and can only be used figuratively. The same may be said of the term 

 " ribs ". In many instances the strands in question, of course, do present the 

 appearance of ribs, and the whole arrangement of them in a blade may be 

 compared with a skeleton upon which the soft portions are attached. We even 

 speak of " leaf -skeletons ", an expression which seems justifiable, since by 

 removing the soft portions a white framework is obtained exhibiting a great 

 analog}^ to the bony skeleton of an animal body. Thus if the blades of green 

 foliage-leaves are allowed to macerate for some time in water, the epidermis 

 and thin-walled gi-een tissues decay, while the tougher strands remain intact; 

 if these leaves are now dried and brushed, all the soft disintegrated parts are 

 removed, and only the skeleton of the leaf remains, in which, as in the 

 skeleton of an animal, larger and smaller structures, may be recognized, con- 

 nected tosfether in the most varied manner. But from the fact that most of 

 the strands, together with those cells which serve to strengthen the whole 

 blade, also contain conducting tubes; that many of them indeed consist only of 

 conducting vessels, it is hardly permissible to speak of skeletons, or to apply 

 the term " ribs " to the strands so beautifully interlaced. Finally, the name 

 " nerves " is still more xmfortunately chosen, for the strands of leaf -blades have 

 no resemblance to animal nerves, either in structure or function. Consequently 

 this designation must be also condemned, although it is the one most often 

 employed by descriptive botanists. 



It is simplest and most correct to call the structures in question what they 

 really are, viz. strands, strands consisting of elongated and fibrous cells, which 

 are combined in the most diverse ways with tubular and pipe-like vessels, and 

 whose elements serve partly for the conduction of fluid materials to and from 

 the green tissues, and partly to afford the necessary protection to the whole 

 blade — protection against strain, pressure, and bending, according to the need 

 of the moment. 



In looking for the origin of the strands on a leaf-blade, we are always 

 directed to the stem from which the leaf in question springs. In other words, 

 the first trace of those strands, which traverse the leaf-blade as a richly-articu- 



