This section is from the "The elements of drawing & the elements of perspective" book, by J. M. Dent & Sons. Also see Amazon: The Elements Of Drawing & The Elements Of Perspective.
You must now therefore have recourse to some confused mode of execution, capable of expressing the confusion of Nature. And, first, you must understand what the character of that confusion is. If you look carefully at the outer sprays of any tree at twenty or thirty yards' distance, you will see them defined against the sky in masses, which, at first, look quite definite; but if you examine them, you will see, mingled with the real shapes of leaves, many indistinct lines, which are, some of them, stalks of leaves, and some, leaves seen with the edge turned towards you, and coming into sight in a broken way; for, supposing the real leaf shape to be as at a, Fig. 7.
This, when removed some yards from the eye, will appear dark against the sky, as at b; then, when removed some yards farther still, the stalk and point disappear altogether, the middle of the leaf becomeslittle more than aline; and the result is the condition at c, only with this farther subtlety in the look of it, inexpressible in the woodcut, that the stalk and point of the leaf, though they have disappeared to the eye, have yet some influence in checking the light at the places where they exist, and cause a slight dimness about the part of the leaf which remains visible, so that its perfect effect could only be rendered by two layers of colour, one subduing the sky tone a little, the next drawing the broken portions of the leaf, as at c, and carefully indicating the greater darkness of the spot in the middle, where the under side of the leaf is this is the perfect theory of the matter. In practice we cannot reach such accuracy; but we shall be able to render the general look of the foliage satisfactorily by the following mode of practice.
Gather a spray of any tree, about a foot or eighteen inches long. Fix it firmly by the stem in anything that will support it steadily; put it about eight feet away from you, or ten if you are far-sighted. Put a sheet of not very white paper behind it, as usual. Then draw very carefully, first placing them with pencil, and then filling them up with ink, every leaf mass and stalk of it in simple black profile, as you see them against the paper: Fig. 8. is a bough of Phillyrea so drawn. Do not be afraid of running the leaves into a black mass when they come together; this Exercise is only to teach you what the actual shapes of such masses are when seen against the sky.
Make two careful studies of this kind of one bough of every common tree, - oak, ash, elm, birch, beech, c.; in fact, if you are good, and industrious, you will make one such study carefully at least three times a week, until you have examples of every sort of tree and shrub you can get branches of. You are to make two studies of each bough, for this reason, - all masses of foliage have an upper and under surface, and the side view of them, or profile, shows a wholly different organisation of branches from that seen in the view from above. They are generally seen more or less in profile, as you look at the whole tree, and Nature puts her best composition into the profile arrangement. But the view from above or below occurs not unfrequently, also, and it is quite necessary you should draw it if you wish to understand the anatomy of the tree.
The difference between the two views is often far greater than you could easily conceive. For instance, in Fig. 9., a is the upper view, and b the profile, of a single spray of Phillyrea. Fig. 8. is an intermediate view of a larger bough; seen from beneath, but at some lateral distance also.
When you have done a few branches in this manner, take one of the drawings, and put it first a yard away from you, then a yard and a half, then two yards; observe how the thinner stalks and leaves gradually disappear, leaving only a vague and slight darkness where they were, and make another study of the effect at each distance, taking care to draw nothing more than you really see, for in this consists all the difference between what would be merely a miniature drawing of the leaves seen near, and a. full size drawing of the same leaves at a distance. By full size, I mean the size which they would really appear of if their outline were traced through a pane of glass held at the same distance from the eye at which you mean to hold your drawing. You can always ascertain this full size of any object by holding your paper upright before you, at the distance from your eye at which you wish your drawing to be seen. Bring its edge across the object you have to draw, and mark upon this edge the points where the outline of the object crosses, or goes behind, the edge of the paper. You will always find it, thus measured, smaller than you supposed.
When you have made a few careful experiments of this kind on your own drawings, (which are better for practice, at first, than the real trees, because the black profile in the drawing is quite stable, and does not shake, and is not confused by sparkles of lustre on the leaves,) you may try the extremities of the real trees, only not doing much at a time, for the brightness of the sky will dazzle and perplex your sight. And this brightness causes, I believe, some loss of the outline itself; at least the chemical action of the light in a photograph extends much within the edges of the leaves, and, as it were, eats them away, so that no tree extremity, stand it ever so still, nor any other form coming against bright sky, is truly drawn by a photograph; and if you once succeed in drawing a few sprays rightly, you will find the result much more lovely and interesting than any photograph can be.