718 ERECT FOLIAGE STEMS. 



The limits of this book do not allow me to treat this theme as fully as my 

 inclination and predilection for the relations between art and science would prompt 

 me to do, but as a tree may be sketched on a wall with a few strokes, so I will 

 endeavour to represent the principles of the " habit " in a few words. 



In every tree the position of the buds depends upon the position of the foliage- 

 leaves, and it is evident that the distribution of the lateral twigs proceeding from 

 a branch is also dependent upon the position of the leaves. The correlation between 

 the arrangements of leaves and of branches is therefore the first which has to be 

 considered in explaining the " habit". Like leaves, the branches are either whorled 

 or decussate, or arranged along a spiral line, and it may therefore be said that the 

 branches also exhibit the definite geometrical relations which were described in 

 detail for leaves on pp. 396-407 ; even this fact gives a characteristic stamp 

 to every tree. How very difierent are maples and ashes with their decussating 

 branches, in comparison with elms, limes, and alders, with leaves arranged on the 

 one-half and one-third system, and with beeches, oaks, and poplars characterized by 

 the two-fifths and three-eighths arrangement; they differ not only in detail, but 

 also in the grosser features of the whole tree-crown. Not only are the bare trees 

 in winter-time readily recognizable at a distance by their ramification, but every 

 portion of the leafy crown derives its particular contour in consequence of this 

 branching. Then, again, the size and shape of the foliage-leaves have to be con- 

 sidered in interpreting the habit. This does not imply that the painter should 

 represent the individual leaves, so that they could be recognized, for that would 

 in a picture be undesirable. The significance of the configuration of the single 

 leaves lies rather in the fact that they regulate the form of the whole tree. The 

 boughs and branches of trees with narrow, linear, or needle-shaped leaves have far 

 less to support than those which are adorned with large, flat, extended leaf-blades. 

 Trees of the former class are characterized by their height, of the latter by their 

 width, a difference which appears in the trees of all parts of the world. For 

 example, the difference in the architecture of slender, narrow-leaved eucalyptuses 

 and willows, and the broad-leaved paulownias, catalpas, and planes, with their wide- 

 spreading boughs, is very striking. If we compare the illustrations of oak and fir 

 placed opposite one another on the preceding pages, we notice that the needle- 

 bearing boughs and branches borne by the slender stems of the fir-tree scarcely 

 occupy a third of the space of that taken up by the thick, heavy trunk of the oak, 

 the leaves of which are so much broader. 



A third point which comes under consideration is the light required by the leaves 

 on the lower boughs of older trees. The thicker and more abundant the foliage 

 on the summit or top of the crown, the deeper becomes the shade around the lower 

 part of the main trunk. If the lower boughs are not able to elongate continually 

 by means of new additions they die, together with their shaded foliage, withering 

 up and breaking off" either wholly or in part at the first opportunity and falling 

 to the ground; but if they have this capacity of elongating, they push and extend 

 their leafy branches as far as possible out of the circle of the shadow into the 



