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It should be said that too much heat is quite as objectionable as a 
too low temperature. Of species not adapted to high temperatures the 
Boxelder, Aspen, Yellow and Sweet Birch, the Spruces, Larches, and 
Northern Pines and Hemlock may be mentioned. 
LIGHT. 
It may be safely assumed that all species of trees make their stron- 
gest growth when in the enjoyment of full sunlight, quite free from the 
shade of their fellows. While this is true, certain species can endure 
more shade than others, some even being able to pass their entire 
lives in comparatively dense shade. Almost if not quite all trees can 
withstand more shade during the first few years of their lives than 
subsequently; indeed, to some, notably the conifers, such protection is 
necessary during their infancy. This variability in the amount of 
shade a species can withstand has given rise to the expressions ‘ light 
demanding,” applied to trees which require full light for their develop- 
ment, and ‘*shade enduring,” which are species that can grow for a 
longer or shorter period in the shade of others. The Cottonwood and 
the Scotch Pine are good examples of light-demanding trees, and the 
Beech and Hemlock of shade enduring. 
The relative amount of light required by a species changes with heat 
and moisture; thus in a moist, warm soil an increased amount of shade 
may be endured and permit the assimilation of the greater amount 
of food available. One may have striking examples of the interrelation 
of heat, light, and moisture in the storage of such ornamental plants 
as the Oleander through winter. These plants are grown in large pots 
or tubs, and they may be safely kept in a comparatively dark, cool 
cellar, if at the same time they be given but very little water. If too 
much moisture be given, the plants will rot, and if they be kept too 
warm a long spindling growth will result that will weaken the plant 
almost beyond recovery. If the storage room be light, an increased 
amount of both heat and moisture will be necessary to keep them 
healthy. 
Because certain species, such as the flowering Dogwood, Beech, Sugar 
Maple, and Hemlock of the Appalachian region, are found to endure for 
long periods in the shade of other trees, like the oaks and pines, it 
must not be assumed that the shade is necessary to their best growth. 
Neither is it a reasonable inference that the Hemlock can be grown 
only in the shade because of the disastrous effect upon Hemlock of the 
removal of associated species. In this case it is the sudden increase of 
light and the inability of the species to adjust itself to new conditions 
that frequently results in the death of the Hemlock. Were the pines 
and hardwoods thinned out gradually, affording a slow change extend- 
ing over a period of years, the Hemlocks Would doubtless be benefited 
by the increased light. 
