THE MORPHOLOGY OF WEEDS 



119 



grass leaves are parallel veined, the leaf of the canna has 

 a similar venation. The veins or lines run parallel with 



each other from the 

 base to the end of 

 the leaf. Plants 

 with such venation 

 have a single seed 

 leaf or cotyledon. 



In netted-veined 

 leaves the veins 

 run together or 

 anastomose, form- 

 ing a network, as 

 in the maple, oatc, 

 and potato ; all of 

 our trees have 



netted-veined leaves. 

 Fig. 42- x, tendril of star cucumber. There are t WO 



types of these, the 

 palmately veined, when 

 the veins start from 

 a number of ribs, as 

 in the grape and maple, 

 or pinnately veined, 

 where one rib runs 

 through the leaf from 

 the base to the tip, as in 

 milkweed. 



Leaves are divided 

 into simple and com- 

 pound. In a simple 

 leaf, like the maple, 

 there is a single stalk 

 and a blade. In com- 

 pound leaves there are 



, , a , , Fig. 43. Palmately netted-vemed, 



several leaflets, each compound leaf of horse chestnut. 



