204 Choice of Plant Material 
type, in which, as with the elm, a constant forking into 
equally strong branches takes place; and the polypodial or 
multifarious branching type, to which the majority of trees 
conform. But even this latter, apparently lawless type, has 
points of symmetry; it can be classified and the law of its 
de\clopment recognized. The number and distribution of 
Icng and short shoots, of stout and slender twigs and branches, 
arranged opposite or spirally, the straightness or crookedness 
cf the single limbs, the angle of insertion, the erect, spread- 
ing or more or less pendent habit, are variously possessed by 
the different genera and species, and account for the variety 
of tree crowns; while the relative development in length of 
the bole and branches give rise to the varying outlines: con- 
ical, globular, elliptical, umbrella-shape, vase-shape, and the 
unsymmetrical straggling outline. 
But while we can recognize types to which the species on 
the whole conform, there is individual variety which removes 
single trees more or less from the types, and this fact of 
the variability in form and other characteristics must not be 
forgotten in selecting plant material. 
Not only is there great inherited individual variety in trees 
of the same species, but the height growth, outline, and gen- 
eral form, size of foliage, and even color, are much more influ- 
enced by the soil in which the tree grows than is usually 
realized. 
The great variation which we may observe in this respect 
in trees of the same species is sometimes so astonishing that 
we might be inclined to class them as different species. See- 
ing, therefore, a particularly pleasing form or color in one 
situation, we must not expect that the same effect may be 
duplicated in another quite different situation. 
The same difference, although less striking, is observed 
in the leaf period. Not only general and local climatic con- 
