1388 



AMERICAN FORESTRY 



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, interspersed be- 

 tween the periods of work. Rest periods, however, 

 should not be regarded as synonymous with idleness, for 



JUST BEFORE HEIGHT GROWTH STOPS 



The twigs of Norway Spruce take a decidedly drooping position for a few 

 days just prior to the cessation of height growth. 



they are normal prerequisites to the optimum function- 

 ing of all organisms. Without them no organism can at- 

 tain optimum efficiency nor maintain health. 



Few comprehensive statements can be made regarding 

 the growth behavior of forest trees during the growing 

 season. There is wide divergence between the height 

 growth behavior of Wild Black Cherry, Sweet Buckeye, 

 White Pine, Tulip Tree, and Norway Spruce. Yet, in 

 spite of this 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 maxi- 

 mum which is maintained for a short while, finally falls 

 gradually to a minimum, and then ceases completely. 



The actual growth is, however, less regular than charts 

 indicate, for the rate of growth usually exhibits a certain 

 rhythm or periodicity. It progresses by leaps and bounds 

 alternating with rest periods, which may be of long or 

 short duration. Rest periods of short duration occur 



frequently and at irregular intervals, but are hard to 

 detect with instruments of ordinary precision. Rest per- 

 iods of longer duration are also common and readily 

 measurable. 



The height growth of a Chestnut Oak, Quercus Prinus, 

 tree during the 1918 growing season showed the terminal 

 shoot started to grow on April 17 and continued its 

 elongation until May 23, when the first upward thrust 

 ceased. A resting period of 24 days followed and on 

 June 16 growth was again resumed and continued until 

 July 13, a period of 27 days. The first growing period 

 extended over 34 days during which the terminal shoot 

 elongated a total of 10 inches, that is an average of 

 approximately one-third of an inch per day. This was 

 followed by a cessation of growth for 24 days when the 

 second and final elongation of the season began. The 

 second growing period extended over only 2j days during 

 which the terminal shoot elongated a total of 13.5 inches, 

 that is an average of one-half an inch per day. Such a 

 periodicity of growth is not unusual, but rather peculiar to 



TAKING A DAILY MEASUREMENT OF GROWTH 



The terminal twig of Norway Spruce is the last to begin its elongation. 

 but by the end of the growing season it exceeded all others in length. 

 Some trees grow in height more than one-inch each day during the grand 

 period of growth. 



certain species. Pin Oak, Black Oak, Chestnut Oak, and 

 Pitch Pine frequently begin to place a second growth 10 

 to 25 days after the original growth of the season has 

 ceased. 



The period during spring and summer when height 

 growth does not progress may be regarded as a resting 

 period, a recuperative period, or a period of preparation. 



