112 STRUCTURAL BOTANY. [95, 96. 



Beech, Chestnut. In the Radiate-veined (palmi-veined) 

 leaf, the venation consists of several veins of nearly 

 equal size radiating from the base toward the circum- 

 ference, each with its own system of veinlets. Ex., 

 Maple, Crowfoot. Lastly, the Tripli-^veined seems to 

 be a form intermediate between the two former, where 

 the lowest pair of veinlets are conspicuously stronger 

 than the others, and extend with the midvein toward 

 the summit (see Fig. 319). 



286. In parallel-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, from 

 a rnidvein, as in the Canna, Calla, etc. 



CHAPTER XXI. 



MORPHOLOGY OF THE LEAF CONTINUED. 



287. That infinite variety of beautiful and graceful 

 forms for which the leaf is distinguished becomes 

 intelligible to the student only when viewed in con- 

 nection with its venation. Since it is through the 

 veins alone that nutriment is conveyed for the devel- 

 opment and extension of the parenchyma, it follows 

 that there will be the greatest extension of outline 

 where the veins are largest and most numerous. Con- 

 sequently 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 accordance with 

 this theory, leaf-forms will be classed in respect to 

 their venation. M 



288. Feather-veined leaves. Of these, the follow- 

 ing forms depend upon the length of the veinlets in 



