314 



The Garden Magazine, July, 1922 



which are the bast and the corky formations of the bark. The 

 formation of these durable elements and the way in which the 

 outer dead bark may be recurrently split and patched from 

 within is complicated mechanically, and need not engage us 

 further at the present time. In the development of the original 

 young cells of the seedling, the greater number pass over into 

 permanent form, with the exception of a thin layer between the 

 wood and the bast, and it is upon the activity of this cambium 

 layer, as it is called by the botanists, that the future of the tree 

 depends. 



When the cambium layer is at rest or nearly so, the protoplasm 

 of its minute cells is dense and granular, but when these awake 

 with the advent of spring the cells imbibe such a large propor- 

 tion of water that over ninety-nine per cent, of their substance 

 is made up of this liquid, and when the cambium is in this highly 

 hydrated condition it has but little mechanical resistance and 

 is easily torn or rent so that the bark external to it "slips" and 

 may be easily stripped from the trunk. 



The cells or elements of the cambium are extremely minute 

 spindle (needle-shaped) masses of a grayish, shining, protoplasmic 

 jelly, the length of which may be as much as several hundred 

 times the thickness (see below), and these elements form a layer 

 two to ten deep in thickness over the entire trunk and branches 

 underneath the bark, terminating in little cones or growing 

 points at the tips, which are enclosed in the buds. The spring 

 growth due to the awkening of the tips and the bursting of the 

 buds is one of the most familiar yet one of the most fascinating 

 features of the green life about us. 



The chief business of a tree is to grow and to reproduce. 

 These two departments of its activities are conducted on widely 

 diverging lines, one being carried out in a highly effective man- 

 ner and the other quite regardless of cost or of wasted energy. 



In many plants this extravagance is carried to the greatest 

 possible extreme; thousands of brilliant-hued flowers are de- 

 veloped for a dramatic display advertising the period of fertili- 

 zation, and large colorful edible fruits are perfected later which 

 have but little proven value for the seeds they carry. The 

 country is sown with thousands, perhaps millions, of nuts, 

 acorns, samaras, beans, and seeds year after year, to the end that 

 a single parent tree may be replaced when it 



falls by a young and sturdy successor, or at 



most, a few dozen saplings. & — : — 



In contrast with this wastefulness is the . 

 unseen, quieter construction of new masses 

 of protoplasm, the formation and differen- 

 tiation of additional cells with the resulting 

 visible enlargement of the body which we 

 designate as growth. 



These hidden processes are the intimate 



»» 



Spindle-shaped cells of the cambium of 

 White Pine (Pinus strobus), the division 

 and enlargement of which constitutes 

 the main feature in the growth of a tree. 

 (After drawings by Prof. 1. W. Bailey) 



life of a tree. To record its daily " pulse," to measure the swelling 

 growth in spring, and to write the record of the variations caused 

 by rains, high temperatures and dry days, it was necessary to 

 devise a delicate apparatus, so small that it might be carried by 

 the tree without injury and yet so finely adjusted that its tracing 

 pen would write everything the tree might do in the way of 

 change in size, whether carried out quickly or slowly. 



The dendrograph which I have perfected for this purpose 

 consists essentially of a floating frame of an alloy which does 

 not change with the temperature placed around the trunk. 

 Swelling or shrinking pushes a small quartz rod and moves a 

 pen tracing a line upon a sheet of paper carried by a revolving 

 cylinder. So long as the tree is quiet, as it may be in the dor- 

 mant condition of winter, the pen traces a level line (see opposite). 

 When it awakes it unavoidably moves the pen and writes its 

 story as surely as might the typewriter on which this article is 

 written, and like all living things, it speaks its own language,, 

 which must be translated. 



SUCH a story of the Arizona Ash since March 8th, 1919, now 

 lies before me in the form of slips a foot in length on each of 

 which the tree has written its diary for seven days. This tree 

 stands in the grounds of the beautiful residence of Dr. H. W. 

 Fenner in Tucson, Arizona, where it was placed in 1908, being 

 then two years old. This Ash is native to the region and makes 

 trunks one to two feet in diameter with great spreading crowns, 

 rendering it one of the valuable shade trees of the region (page 

 313). It is usually come upon along the margins of streamways, 

 where the roots may find a good supply of water, and it there- 

 fore is under fairly normal conditions in this irrigated garden. 



When the dendrograph was attached to the tree early in 

 March, 191 9, the staminate flowers (it is a male tree) were al- 

 ready nearly fully developed but the leaves had not yet begun 

 to unfold. For the first few days the pen showed only equali- 

 zing movements, tracing a downward course beginning early in 

 the morning and continuing until late afternoon, at which time 

 a slow increase in size began which continued through the 

 night until the level of the previous morning was reached. In 

 this action is to be seen the fact that a slow stream of water is 

 passing up through the trunk even when 

 it is dormant, being given off by evapora- 

 tion from the leaves. During the warm 

 sunny and windy days the drying out of the 

 branches and trunk carries away more water 

 than is received from the sluggishly acting 

 root system, with a resultant shrinkage. 



The advancing temperatures of spring 

 awaken the cambium and the cells of the 

 growing points not only in the buds but also- 



DENDROGRAPHIC RECORD OF THE ASH, MAY 12 TO MAY 19, 1919 



The ruled sheet is carried along at such rate that every day at noon the pen crosses the curved line carrying figures. A shrinkage has 

 taken place every day at this time, having begun about eight o'clock in the morning and continuing until four or five in the afternoon 



