198 SECTIONAL ADDRESSES 
got to grow normally up to full maturity, and to produce fertile seed, in 
a climate warmer or colder than that of any climate in which it is found 
within its natural range of distribution, then and then only it would seem 
that we could speak of acclimatisation. Trees have a certain amount 
of plasticity and can alter their form, rate of growth, and stature to a 
surprising extent in response to external growth factors, but such reaction 
changes are not permanent and hereditary. Trees vary in their demands 
for light : some are more tolerant of shade than others ; nevertheless, all 
trees will show definite symptoms of want of light if grown in too dense 
shade. Small scanty leaves and needles, thin attenuated twigs, small 
buds, a gradual flattening and broadening of the crown, as well as certain 
internal anatomical changes, are some of the symptoms. In a dense 
forest, trees may pass their lives in varying degrees of overshading and yet 
we find that individuals, or their seedlings if any, are always ready to 
respond by normal growth to increased light intensity. There is no trace 
here of reaction changes to light becoming permanent and hereditary. 
Again trees, some at least, can grow in a fairly wide range of soils, but in 
no case, however gradual the transition, can we induce the deep-sinking 
tap-rooted oak to grow normally in shallow soil. Nor by the reverse 
process can we get the shallow-rooting spruce to form a deeper root 
system by cultivating it on deep soils. In these and other cases, the 
results would be very valuable, but all the tree does is to temporarily 
react in growth and habit according to variations in the soil. 
In forestry the long period which must elapse between the establish- 
ment of a crop and its final harvesting at maturity makes it imperative 
that we should use every endeavour to secure the best types of trees 
suitable for the concrete conditions of the localities in which they are to 
be grown. If a wrong species is chosen at the start—that is, a species 
unsuited to the soil or climate—and in mixed woods, if a wrong combina- 
tion of species is adopted in their formation, then no amount of skill, care, 
and attention on the part of the forester can remedy the defect or make 
full use of the productivity or growth factors of the locality. In cultivating 
his crops the forester must always keep in mind that the ultimate success 
of his efforts is determined by rate of growth combined with the useful- 
ness and volume of the timber produced. This again brings him into 
close contact with the botanist. Among species of trees, apart from 
varieties and sports or mutations, no two individuals are absolutely 
identical, in spite of all outward resemblance. There are differences in 
rate of growth ; commencement and duration and finish up of seasonal 
vegetation ; flower, fruit and seed production. All these may vary in 
time from a few days up to as much as oneor twoweeks. These differences 
may occur in all soils and in all climates. In both the artificial and the 
primeval forest it can be detected among trees of the same species, growing 
side by side on the same soil and sprung from seed of the same parent 
tree. Individuals from the same seed may show differences in stem 
quality, branch formation and crown balance, due to some internal 
impulse, which is independent of soil or climate. Some individuals 
produce straight cylindrical stems, others bent, twisted and crooked 
stems ; some have an inherent tendency to fork and produce double 
