64 



FOEM OB FIGUBB. 



269. Of the reticulate venation, the student should carefully note 

 three leading forms, the feather-veined, the palmate-veined, and the 

 triple-veined. 



The feather- veined (pinni-veined) leaf is that in which the venation 

 consists of a midvein giving off at intervals lateral veinlets and branch- 

 ing veinulets. Ex. beech, chestnut. 



260. In the eadiatb-veined (palmi-veined) leaf the venation con- 

 sists of several veins of nearly equal size, radiating from the base 

 towards the circumference, each with its own system of veinlets. Ex. 

 maple, crow-foot. 



261. The tmpli-veinkd seems to be a form intermediate between 

 the two others when the lowest pair of veinlets are conspicuously 

 stronger than the others above them towards the apex, extending with 

 the midvein towards the summit. 



262. In paeallkl-veined venation the veins are either straight, as 

 in the linear leaf of the grasses, curved, as in the oval leaf of the 

 orchis, or transverse as in the Canna, Calla, <fec. 



FOKM OR FIGUEE. 



U4 



no 118 



Forms of leaves. 110, Ehododendron maximum. HI, Alnus glutinoaa (cult). 112, Poly- 

 gonam sagittatum. ■ 118, Pawpaw. 114, Impatlens fulva. 115, Coltis Americana. 116, Circaea 

 Lutetiana. 117, Catmint. 113, Solidago Canadensis — a triple-veined leaf. 



263. That infinite variety of beautiful and graceful forms for which the leaf is 

 distinguished heoomes intelligible to the student only when viewed in connection 

 with its venation. Since it is through the veins alone that nutriment is conveyed 

 for the development and extension of the parenchyma, it 'follows that there will Be 

 the greatest extension of oaiUne when tho veins are largest and most numerous. 

 Consequently the form of the leaf will depend upon the direction of the veins and 

 the vigor of their action in developing the intervening tissue. In our description 



