Floristik, Geographie, Systematik etc. 299 



The processes of primary thickening and secondary thickening 

 overlap, and both may be going on in closely neighboring spots in 

 the tree at the same time. 



Growth in white pine is divisible into a) growth without cell 

 division and b) growth with cell division. The first begins as early 

 as March and the Clements concerned (phloem) increase in radial 

 diameter from 50 to over 100 per cent, The awakening of growth 

 is due apparently to the rise of soil water with an accompanying 

 increase in temperature. 



Growth by cell division begins during the last half of April. At 

 the Start it is very rapid, and more Clements are formed at the in- 

 side of the cambium than at the outside. The formation of new 

 xylem Clements 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. 



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. 



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 foUow no definite law. 



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 irregulär at different heights in the 

 tree, but the cambium tends to even up discrepancies as the sea- 

 son progresses. The irregularities of growth are manifested not 

 only in the actual dimensions of the newly formed tissues, but also 

 in the xylem Clements. Wide discrepancies may occur in closely 

 neighboring trees; in general, larger differences may be expected 

 the greater the disparity in age. 



Growth is first retarded in the Upper portions of the tree; it 

 may continue vigorously below for some weeks longer. 



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. 



The total growth of white pine extends over a period of 5,5 

 months, growth by cell division between 4 and 5 months. 



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. 



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. 



White pine has long roots and short roots. Only the first elon- 

 gate to any extend and often are in symbiosis with mycorhiza. 

 Growth in length begins during the last half of April, in some 

 cases even earlier; no reliable data were obtained regarding its 

 cessation. Secondary growth occurs during the first season and 

 proceeds in the usual way. - Jongmans. 



