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 t}^e, has 

 points of symmetry; it can be classified and the law of its 

 development recognized. The number and distribution of 

 long and short shoots, of stout and slender twigs and branches, 

 arranged opposite or spirally, the straightness or crookedness 

 of the single hmbs, 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; w^hile the relative development in length of 

 the bole and branches give rise to the varying outlines: con- 

 ical, globular, elhptical, umbrella-shape, vase-shape, and the 

 unsymmetrical straggling outline. 



But while we can recognize types to which the species on 

 the w^iole 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 he 

 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- 



