630 SCALE-LEAVES, FOLIAGE-LEAVES, FLOUAL-LEAVES. 



Those lateral stramls are termed reticulate (dictj'odronious), -wliich Ijreak up 

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

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

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

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

 moi-e vigorous than the others. The leaf of the Wild Pear (Pyrus conimtonis) 

 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 (bracliydodromous) 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 (Rhamnus Frangula and 

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

 see fig. 149^^), in many species of dock and nightshade, and especiallj^ 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 {Symphytwni and Pidniono.ria) 

 tliese loops are developed at some little distance from the margin of tlie 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 suddenlj- 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 Myrtace», 

 hut many tropical Morese are also distinguished by it, and the leaves of the 

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

 strands (see fig. 1491"). 



Arched strands (kamptodromous) ai-e those which run out from their 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 (Cornus 

 niMs), 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 



