70 



INTRODUCTION TO BOTANY 



leaves with the veins running somewhat parallel to each othsr. 

 Sometimes, as in the canna (fig. 50), the veins run both ways 

 from a midrib, but oftener, as in corn and the other grasses, 

 the veins run from the base to the tip of the leaf. This latter 

 system of veining is most commonly found in long, narrow 

 leaves. Most dicotyledons have net-veined leaves. These 

 are of two types : those like the leaf of the willow, oak, and 



FIG. 50. Parallel-veined 



leaf of canna, veins 



running from midrib 



to margin 



FIG. 51. An apple twig in the autumn 

 Alternate arrangement of leaves 



peach, with the smaller veins running both ways from a mid- 

 rib; and those like the geranium, hollyhock, and cucumber, 

 with the veins radiating from the base of the leaf, like the 

 sticks of a fan (fig. 49). Net-veined leaves with feather- 

 like veining frequently have a length several times as great as 

 their width, while those with fan-like veining are often round- 

 ish in their general outline. Whatever the shape of the leaf, 

 the veining is so disposed that a ready means of distribution 

 throughout the leaf is offered to the water brought into it through 



