The Garden Magazine, July, 1922 



315 



in the root-tips, and new cell-masses are formed which may take 

 the form of additional wood and bast, and the thickness of the 

 trunk may increase by a minute accretion every day of the 

 growing season. • When this is taking place, the pen makes 

 movements of much wider amplitude during the course of the 

 days, as may be seen by the record of a May day shown on page 

 314. I f we examine the record closely, we may see that beginning 

 about four or five o'clock in the afternoon the pen commences 



THE DENDROGRAPH AT WORK 



Attached to a Monterey Pine with the pen 

 tracing the daily variations in size of the 

 trunk. Cylinder and needle are protected from the inclemencies of 

 weather by a box which fits snugly over both and is held in place by a 

 bracket fastened to the trunk above 



to rise on the sheet and continues to do so until about eight 

 o'clock the next morning. Thus on Tuesday morning the pen 

 had moved upward about twenty millimeters on the sheet, and 

 as the instrument was set to amplify growth twelve times, the 

 trunk was actually about a sixteenth of an inch thicker on 

 Tuesday morning than at sunset on Monday evening. Some of 

 this gain, however, was simply water and about half of it was 

 lost during the day, but a similar gain was made Tuesday night, 

 only part of which was lost during the day. 



Likewise some of the gain of Wednesday night was lost on 

 Thursday, but it will be noted that the pen rose higher each day 

 so that on Monday morning the end of the line tracing the 

 variations in the trunk stood forty millimeters higher than on 



the previous Monday at the same time, denoting that the trunk 

 had made an increase of an eighth of an inch in thickness, as 

 much as many Oak and other hardwood trees make in an entire 

 season. The records for the following weeks show that the rate 

 became less and less with the advance of the summer until on 

 August 25th growth came to a standstill, although the tempera- 

 ture was still favorable and the soil moisture content was high. 

 Later and separated by intervals of a few days were feeble im- 

 pulses of growth lasting for a week perhaps, which some writers 

 believe to be due wholly to formation of bast and not to wood. 

 Finally in the latter half of November the leaves began to drop, 

 the trunk became quieter, and its daily variations equalized as 

 shown in the diary from November ioth to 17th (see below). 



AS ONE follows these records from day to day, many features 

 jt\ of the weather may be connected directly with these 

 changes. Looking closely at the record for the week in May, 

 the reader may see that the inked line appears broadened es- 

 pecially in the bottom parts of the loops, a feature due to high 

 winds which increases the water loss from the leaves and 

 branches and an increased shrinkage of the trunk. 



Early in April a storm brought a heavy rainfall which fell as 

 snow on the neighboring mountains and caused a drop in tem- 

 perature so that a thermometer thrust under the bark showed 

 the cambium had a temperature not over 50 degrees which 

 stopped growth for five days, when rising temperatures again 

 caused the pen to rise on the sheet. 



The total increase in the trunk during the growing season 

 of something over five months was about an inch and a half in 

 diameter or a formation of an encircling woody layer three- 

 quarters of an inch in thickness. 



The observer who expects rigidly regular habits in growth 

 will be due many surprises when his measurements are made 

 with the dendrograph, for, as illustrated by the effects of the 

 storm just cited, the tree is delicately adjusted to its environ- 

 ment and the forester who has studied the annually formed 

 layers which appear as rings on the end of a log or stump knows 

 that the amount of wood varies widely year by year; that none 

 may be formed in some seasons while two or even three appear 

 in the record of other years. 



The Ash tree which forms the subject of this article exhibited 

 this specialization by deferring the beginning of growth in 1920 

 until June, the period of enlargement ending in midsummer, 

 much earlier than in 1919, with a total formation of wood not 

 more than a third that of the previous years. It has been fitted 

 with a new instrument of improved design and the story which 

 it has written for these two years of its life is being continued 

 day by day. 



RECORD OF THE ASH IN AUTUMN, NOVEMBER 10 TO NOVEMBER 17, 1919 



During this period when the leaves were coloring and falling off the daily variations were very 

 small; note on opposite page the much greater fluctuation recorded in May of the same year 



