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 prevaiHng 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. 



1 1 . Xylem formation go^s on very sluggishly in all parts of the 

 tree (the terminal, leader excepted) until late September and early 

 October, phloem development as lofig 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 i ; 

 needle growth may continue until August 15 or even later. 



