FORMS OF LEAVES. Wr 
of the decay of the green substance of the leaves 
from long exposure on the wet ground; but the full 
grown leaf of the Poplar and of some other trees, if 
soaked in water for two or three weeks and then care- 
fully cleaned with a camel’s hair brush, will yield a 
good frame-work of the leaf; but in making the 
experiment choice should be made of only such leaves 
as are free from holes in the blade, or from spots or 
blisters, as these last will not come off clean, but will 
break away during the preparation. The veins not only 
give the blade its form, but as they are the vessels of 
the stem which pass out into the blade and back again 
into the stem through the leaf-stalk, they serve also 
to convey the proper juices of the plant. 
9. The leaf-stalk or petiole is almost always united to 
the stem by a joint, as may be seen by breaking it off 
from the stem; on which the marks or scars of the 
leaves which have fallen off can frequently be found - 
(f. 2.8.).. The leaf-stalk is not present in all leaves, 
and then the blade joins the stem at its base, and is 
called a sessile leaf (f. 3.); while one with a leaf-stalk 
is termed a stalked or petiolate leaf. In some leaves, 
as for instance in the Rose and Violet, where the 
leaf-stalk joins the stem, two small leafy organs are to 
be seen, one on either side, these are considered to be 
additions to the leaf, and are termed stipules (pl. 8. 
f. 1. st.): they are sometimes very large and are 
mistaken for the leaves, as in the Violet and Hearts- 
ease (pl. 2. f. 4. st.). 
10. Leaves assume very varied forms and appearances, 
and yet by their forms are plants often recognized and 
