GROWTH AND WORK OF PLANTS 



the vascular system of the stem. Water and food substances are 

 carried from the stem through them and distributed to all parts of 

 the leaf, and the food assimilated in the leaves is carried back 

 through the bast portion of the bundles to supply the growing 

 parts of the stem and roots. The " veins " also assist in giving 

 firmness and support to the thin and broadly expanded blade. 



119. Kinds of venation in leaves. In general there are two 

 kinds of venation presented by leaves, which in general are cor- 

 related with certain characters of relationship noted in stems and 

 seedlings. The venation is either parallel or netted (reticulate), 

 so that we speak of parallel veined leaves and netted veined leaves. 

 In the former the veins are long, regular and nearly parallel and 

 are characteristic of most monocotyledons, as in the corn, the 

 cereals, other grasses, palms, etc. There are two kinds: First, 

 those in which the veins all run from the base 

 to the apex of the leaf; second, the pinnately 

 veined, or feather veined, those in which there is 

 a mid-vein running from the base to apex, and 

 the lateral veins are parallel and run from the 

 mid-vein to the margin, as in the pickerel weed 

 and the banana. Parallel venation, however, is 

 not characteristic of all monocotyledons, since 

 the leaves of the Indian turnip, or Jack-in-the- 

 pulpit, have netted veined leaves. In netted 

 veined leaves, the veins do not run with such 

 regularity, the main veins diverge more or less 

 and their branches finally anastomose into a 

 very intricate network. There are also two 

 kinds of netted veined leaves, the palmate and 

 the pinnate. Palmate leaves are those in which 

 the main veins spring from the petiole and 

 then diverge something like the digits of the 

 hand (palm) toward the margin of the leaf, as in 

 the maple. In pinnate leaves there is a main 

 vein which extends from the petiole directly through the middle 

 line of the leaf, and the main branches from this arise at nearly 



Fig. 66. 



Leaf ot rubber 

 plant, a pinnately 

 veined leal, edge 

 plane. 



