THE LEAF 67 
ators of the two previous fractions and similarly with 
the denominator. 
By means of these various arrangements the plant is 
enabled to expose its leaves, so that each gets a proper 
amount of illumination, and thus carries on the work of 
carbon assimilation satisfactorily. 
36. Venation.—The vascular bundles of the root and 
stem are continued into the leaves in the form of 
strands called Verns. They project above the leaf tissue, 
and give strength and support to the flat blade. They 
bring watery solutions from the root, and carry away 
the elaborated food products produced during carbon 
assimilation. Veins round the margin of a leaf often 
prevent it from being torn by the wind, e.g. Senecio. 
Frequently the mid-vein is the most strongly developed, 
and is spoken of as the Mipris. Lateral veins branch - 
out from this chief vein. 
There are two chief kinds of venation :— 
(a) Parallel venation (fig. 43 pb), typical of Mono- 
cotyledons. 
(b) Reticulate, or netted, venation (fig. 43 B), typical 
of Dicotyledons. 
Tn parallel venation the veins run either approximately 
parallel with each other, joining on to a midrib, or in 
curves converging at the base and apex of the leaf, e.g. 
grasses. There is no irregular network between the 
veins. 
Tn reticulate venation the veins branch off from one 
another, ultimately forming a fine, close, irregular net- 
work. If in reticulate venation there is a midrib from 
which several lateral veins branch off we have pinnately 
5 * 
