12 BULLETIN 13, U. S. DEPARTMENT OF AGRICULTURE. 
ment. It succumbs to shade much more quickly than hemlock, 
spruce, beech, or maple, but needs less light than red, pitch, or jack 
pine, gray birch, or aspen. 
The less light a tree receives the slower will be its growth, and if 
shaded beyond a certain point it will die, practically from starvation. 
A suppressed tree to which light is admitted will respond in a greater 
or less degree, according to the length of time it has been suppressed, 
by putting forth new foliage and increasing its rate of growth. White 
pine does not possess the power to recover from suppression to the 
extent shown by hemlock, spruce, or fir, which will exist for years 
under heavy shade, and then, with the admission of light, spring at 
once into rapid, vigorous growth. If not too long suppressed, white 
pine will usually recover to some extent when released, though its 
subsequent growth is apt to be less thrifty than that of unsuppressed 
trees. 
The trees more tolerant of shade naturally produce more foliage 
and themselves cast more shade than those less tolerant, and it is 
for this reason that white pine seedlings under maple, beech, hem- 
lock, or even heavy white pine crowns, can not grow. Under the 
light shade of aspen, paper birch, or other intolerant trees young- 
white pine often receives just enough light to keep it alive and to 
stimulate a rapid height growth, which results if the soil is good 
enough, in its eventually overtopping and displacing the other 
species. When mixed with heavy foliaged hardwoods or hemlock 
white pine crowns almost always project above the general level of 
the crown cover. In such stands the pine is able to reproduce itself 
only when its seeds fall in chance openings large enough to admit 
full light during the period necessary for the tops of the young trees 
to reach the level of the crown cover. 
Since white pine is more tolerant of shade than is red pine it is 
able to grow in much denser pure stands and hence will produce a 
greater amount of wood per acre. 
FORM. 
Young white pines have a symmetrically conical form, due in large 
part to the fact that the branches grow in whorls. A whorl of 
branches marks each season's growth, so that two contiguous whorls 
afford a means of determining the height growth for a given year, and 
all the whorls together the approximate age of the tree. Each suc- 
cessive whorl shuts off light from the ones beneath, and these must 
increase in length if they are to continue to function. In the stand 
this increase is checked by the branches of adjacent trees, while in 
the open it is limited only by natural forces, chiefly gravity. In 
consequence, the crowns of open-grown trees are often broad pyra- 
mids reaching close to the ground. 
