FOLIAGE LEAVES: FUNCTION, STRUCTURE, ETC. 35 
B. Structure of foliage leaves 
28. Gross structure, It is evident that the essential part 
of a foliage leaf is its expanded portion or Uade. Often the 
leaf is all blade (see Figs. 7, 
8, 18) ; frequently there is a 
longer or shorter leaf-stalk 
(petiole) which helps to put 
FIG. 25. Two types of leaf venation. The figure to the left is a leaf of Solomon's 
seal (Polygonatum), and shows the principal veins parallel, the very minute cross 
veinlets being invisible to the naked eye, being a monocotyl type. The figure to 
the right is a leaf of a willow, and shows netted veins, the main central vein (mid- 
rib) sending out a series of parallel branches, which are connected with one another 
by a network of veinlets, being a dicotyl type. After ETTINGSHAUSEN. 
the blade into better light-relation (see Figs. 1, 9, 17, 20, 
26); and sometimes there are little leaf -like appendages (stip- 
ules) on the petiole where it joins the stem,, whose func- 
tion is not always clear. Upon examining the blade it 
is seen to consist of a green substance through which a 
