General Considerations 205 
ditions, but also local soil conditions will cause one tree 
to bud out earlier and retain its foliage longer than another 
tree of the same species. That the length of leaf period is a 
habit capable of inheritance is proved by the fact that sev- 
eral of the exotics which are frequently planted have invari- 
ably a longer leaf period than native species of the same 
genus; the European elms, linden, and maples are examples. 
Another very important point, also often overlooked, is 
that the form of crown changes from the young to the old 
tree: there is a beauty of youth and a beauty of maturity, 
while adolescence is often marked, as in man, by awkward 
and unsatisfactory looks. This is especially the case with 
conifers; for the change from the shapely conical young form 
to the broad stately umbrella-shape or the compactly globular 
or ascending rhomboidal form of old age, interposes a less 
pleasing, longer or shorter, intermediary stage. The descrip- 
tion of the outline or form of a tree can therefore refer only 
to one period of its life, usually the mature stage. 
In selecting rare species which nurserymen are apt to prop- 
agate by grafting on other stocks, it should not be over- 
looked that these stocks may produce undesirable results: 
a different rate of growth may cause bulging at the juncture, 
the lower trunk being either more rapid or less rapid than 
the graft in gaining diameter, or the foliage may revert 1o 
that of the mother stock, etc. Hence, in purchasing such 
grafted trees we must assure ourselves that experience has 
proved the stock upon which the graft is made as trust- 
worthy. 
The same disappointment which we may experience in 
the form development, by virtue of unsuitable soil conditions 
may, of course, extend to the shading value and to the rate 
of growth. The tree which in a rich soil developed a mag- 
nificent canopy of foliage will be scantily furnished in a 
