FOLIAGE AND SCALE LEAVES. 



57 



tions exist. In the sunflower, for example, there is a well- 

 marked midrib, but the pair of lateral veins next the base are 

 much stronger than the remainder. Exceptional dicotyledons 

 are known in which the venation is more or less parallel. The 

 wild plantains {Plantago) illustrate this. In them a number of 

 strong veins take a curved course from base to apex, having 

 between them, however, a typical network formed by small 

 veins. 



The general shape or form of the lamina is correlated with the 

 venation. Monocotyledons have generally leaves with simple 

 outlines, which are longest when basal- veined. In dicotyledons 

 long and short forms are associated respectively with pinnate 

 and palmate venation. Details will be given below. 



It may be noted, as a general rule, that the most complicated 

 outlines occur in small herbs, especially when these occur in 

 crowded situations. The largest leaves are also, in many cases, 

 found nearest the ground. The leaves of the same plant are 

 by no means uniform either in shape or size. This is especially 

 noticeable in herbs. Take, for example, a tall buttercup plant. 

 The lowest, so-called radical leaves, are here the largest and most 

 complicated. They*gradually pass into smaller and less compli- 

 cated upper leaves. Much greater uniformity is found among 

 the leaves of trees. 



It is not possible to make any exact classification of the in- 

 numerable kinds of general outline found among leaf-blades. We 

 may, however, distinguish between forms of fairly equal breadth, 

 or broadest in the middle, and those with broader base or apex. 



fig. 



4. — Oblonsr 

 Leaf. 



Fig. 



5.— Spathulate and 

 Oval Leaves. 



FIG. 16.— Rounded and 

 Arrow-shaped Leaves. 



In the first case, we can gradually pass from the needles of the 

 fir to broader grass leaves, and so through oblong (fig. 14), oval 

 (fig. 15), and rounded (fig. 16) forms to circular ones (fig. 17). 

 Where the blade is broader at the base, the form may distantly 

 resemble that of a lance-head, an egg, &c, hence receiving the 

 name of lanceolate (fig. 18), ovate (fig. 19), &c. Very commonly 

 the base is notched, and projects on either side of the leaf- stalk 

 as a more or less prominent lobe of various form. Heart-shaped 



