368 RELATION TO ENVIRONMENT. 



there are short shoots bearing the needle leaves), whether on 

 the main axis or on the lateral branches, marks a year, the new 

 branches arising each year at the end of the shoot of the previous 

 year. The rate of growth is sometimes as high as twelve to 

 twenty-four inches or more per year. 



The spruces form a more perfect cone than the pines. The 

 long branches are mostly in whorls, but often there are interme- 

 diate ones, though the rate of growth per year can usually be 

 easily determined. In the hemlock spruce, the branching is 

 distributed. The larch has a similar mode of branching, but it 

 is deciduous, shedding its leaves in the autumn, and it has a tall, 

 conical form. 



It would seem that trees of the cone type possessed certain 

 advantages in some latitudes or elevations over other trees, 

 (i) A conical tree, like the spruces and larches and the pines, 

 and hemlocks also, before they get very old, meets with less injury 

 during high winds than trees of an oval or spreading type. The 

 slender top of the tree where the force of the wind is greatest 

 presents a small area to the wind, while the trunk and short 

 slender branches yield without breaking. Perhaps this is 

 one reason why trees of this type exist in more northern latitudes 

 and at higher elevations in mountainous regions, and why the 

 spruce type reaches a higher latitude and altitude even than the 

 pines. (2) The form of the tree is such as to admit light to a 

 large foliage area, even where the trees are growing near each 

 other. The evergreen foliage, persistent for several years, on 

 the wide-spreading lower branches, probably affords some pro- 

 tection to the trees since this cover would aid in maintaining a 

 more equable temperature in the forest cover than if the trees 

 were bare during the winter. (3) There is less danger of injury 

 from the weight of snow since the greater load of snow would lie 

 on the lower branches. The form of the branches also, espe- 

 cially in the spruces, permits them to bend downward without 

 injury, and if necessary unload the snow if the load becomes too 

 heavy. 



717. The oval type. This type is illustrated by the oak, chest- 



