238 BOTANICAL GAZETTE [MARCH 
new xylem elements follows the same order as in pitch pine, that 
is, it begins first in the bole at some distance below the apical 
shoot and spreads upward and downward. As a result, growth 
at the base of a tree may begin several weeks later than in the 
crown. 
7. The awakening and rapidity of growth is dependent on three 
factors, moisture, available food (reserve), and temperature. 
The first two are at an optimum in the spring; the amount of 
growth therefore is directly proportional to prevailing temperatures. 
8. The intensity of growth is a variable factor which changes 
from day to day and even within a single day. Two periodic 
optimums of growth intensity occur, one during May and early 
June, the second in July and August. These vary from time to 
time at a given height in the tree and follow no definite law. 
9. The amount of growth at a definite time and place in the 
tree is equal to the sum of the prevailing growth intensities by the 
time each was in force. It is very irregular at different heights in 
the tree, but the cambium tends to even up discrepancies as the 
season progresses. The irregularities of growth are manifested 
not only in the actual dimensions of the newly formed tissues, but 
also in the xylem elements. Wide discrepancies may occur in 
closely neighboring trees; in general, larger differences may be 
expected the greater the disparity in age. 
10. Growth is first retarded in the upper portions of the tree; 
it may continue vigorously below for some weeks longer. 
11. Xylem formation goes on very sluggishly in all parts of the 
tree (the terminal leader excepted) until late September and early 
October, phloem development as long as temperature permits. 
12. The total growth of white pine extends over a period of 
5.5 months, growth by cell division between 4 and 5 months. 
13. Late wood formation begins during the first half of August, 
it is associated with a decrease in growth intensity and begins first 
in the higher parts of the tree. 
14. Elongation of new shoots and leaves is simultaneous and 
begins in early May; it manifests itself only after xylem formation 
has begun. Growth in length in the shoots ceases about July 1; 
needle growth may continue until August 15 or even later. 
