630 SCALE-LEAVES, FOLIAGE-LEAVES, FLORAL-LEAVES. 



Those lateral strands are termed reticulate (dietyodromous), which break up 

 into a delicate net-work soon after their origin from the primary strand, or 

 at least before they have reached the margin of the blade. The meshes of tlie 

 net-work are of almost equal size, so that it is impossible to distinguish in the 

 confusion of small strands near the margin of the blade any particular one 

 more vigorous than the others. The leaf of the Wild Pear (Pyrus communis) 

 is given as an example of this form in fig. 149 ^. The same distribution of 

 strands, however, is found in very many other plants allied to pear-trees, as 

 also in willows, rhododendrons, and species of barberry and sage. 



The lateral strands called looped (brachydodromous) run fairly straight and 

 distinct towards the margin, but before reaching it they bend round in a 

 graceful sweeping curve, towards the apex, uniting with the next lateral strand 

 above, and with it form a loop. Such loops can always be seen standing 

 plainly out from the delicate net-work of small strands, and the arrangement 

 may be recognized at the first glance. It is observed in the leaves of the 

 Mahaleb and common Cherry, in the Buckthorn (Rham^nus Frangula and 

 Wulfenii, see fig. 149^), in myrtaceous plants {Myrtus, Metrosiderus, Eugenia, 

 see fig. 149^^), in many species of dock and nightshade, and especially in 

 rough -leaved plants (Boraginacese). The net- work of fine strands inserted 

 between the laterals is often so delicate that it is scarcely visible to the naked 

 eye, and then only a series of bold loops, like arcades, is to be seen in each 

 half of the leaf. In the Comfrey and Lungwort {Symphytum and Pulmonaria) 

 these loops are developed at some little distance from the margin of the leaf- 

 blade. In the cherry and buckthorn, on the other hand, the loops are quite 

 close to the margin. The lateral strands are frequently very delicate, and extend 

 in a straight line from the primary strand right up to the margin, when they 

 bend suddenly round, like a knee, almost forming a right angle. The outer 

 limb of this right angle then runs parallel to the margin, and unites with 

 the knee of the next upper lateral strand. In this way we have a strand 

 running parallel with the leaf -margin connected with the central primary 

 strand by cross-ties. This looped form occurs very regularly in the Myrtaceae, 

 but many tropical Moress are also distinguished by it, and the leaves of the 

 Forget-me-not (Myosotis) also exhibit this peculiar arrangement of lateral 

 strands (see fig. 149 ^°). 



Arched strands (kamptodromous) are those which run out from tlieir place 

 of origin on the main strand towards the margin of the leaf, which, however, 

 they never reach, but turn in an arch towards the leaf -apex, and there lose 

 themselves without forming definite loops. As a rule, the places of origin are 

 crowded together in the lower half of the main strand, and the two uppermost 

 arched lateral strands then inclose an oval central area. The Cornel {Gornus 

 mas), illustrated in fig. 149 ^, is chosen as an example of this form. 



Those lateral strands are called undivided (craspedromous) which run in a 

 straight line from the main strand to the margin and there terminate. They end 



