LEA VES, THEIR FORM AND MOVEMENT 



79 



Some of these veins are quite large and prominent, while 

 others are smaller and less conspicuous. Within the veins 

 are the vascular bundles, which are continuous through the 

 petioles with the vascular system of the stem (paragraphs 102, 

 104). 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. 



124. Kinds of venation in leaves. In general there are 

 two kinds of venation presented by leaves, which are corre- 

 lated 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, 



J Leaf of rubber plant, 



since the leaves of the Indian turnip, or a pinnately veined leaf, 



edge plain. 



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 

 unite 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 



Fig. 69. 



