Canadian Foresir}) Journal, September, 1919 



353 



HOW TREES OFTEN TAKE A HOLIDAY IN 



EARLY SUMMER AND LATER RESUME 



THEIR JOB OF GROWING. 



The terminal twig grew 27 days, then rested for 



23 days, and again resumed gro\vtli for about 25 



days. The iminature leaves indicate tlie portion of 



the twig wliicli was developed during the second 



period of growth. 



tinctive inherent growth characteristics. Some 

 place their growth without a break, while others 

 place it by leaps and bounds alternating with 

 rest periods. In this respect the method of 

 working followed by trees, and growth surely is 

 work, differs little from the methods of other 

 organisms, including man. Rarely does any 

 organism work continuously, but rest periods 

 are usually, and sometimes frequently, inter- 

 spersed between the periods of work. 



Few comprehensive statements can be made 

 regarding the growth behavior of forest trees 

 during the growing season. Yet, in spite of 

 wide divergence the fundamental features of 

 the growth procedure throughout the growing 

 season may be summarized as follows: Growth 

 begins slowly, after a variable period rises 

 rapidly, then reaches a maximum which is 

 maintained for a short while, finally falls gradu- 

 ally to a minimum, and then ceases completely. 



The period during spring and summer when 

 height growth does not progress may be regard- 

 ed as a resting period, or a period of prepara- 

 tion. The trees apparently rest, but in reality 

 they are preparing for the next upward thrust 

 which may be longer than the original advance 

 Furthermore, the writer believes that the re- 

 curring rest periods may become a rather fixed 

 and regular feature of the growth of certain 



species. This is certainly true in the case of 

 normal young Pitch Pine in the vicinity of 

 Mont Alto, which exhibits annually a ces — 

 sation of growth for a qeriod of 2 to 3 weeks. 

 Greater Growth by Night. 



The rate of tree growth not only fluctuates 

 throughout the growing season, but also dur- 

 ing each day. The maximum growth usually 

 occurs late at night, apparently after the pre- 

 paration and translocation of food and other 

 essential materials becomes less active, and the 

 minimum growth falls in the afternoon of each 

 clear day when the greatest activity in the manu- 

 facture of starch and sugar is in operation. 



About twenty trees of each of the four spec- 

 ies given in the following tabulation were meas- 

 ured regularly at 7.30 p.m. and 7.30 a.m. for 

 a specified period. The derived results for 

 height growth during the day and at night are 

 given in the following tabulation: 



Species. Day Night 



Tree of Heaven 35 p.c. 65 p.c. 



Tulip Tree 40 p.c. 60 p.c. 



Norway Spruce 18 p.c. 82 p.c. 



White Pme 39 p.c. 61 p.c. 



Average 33 p.c. 67 



p.c. 



