408 Forestry Quarterly. 



summer layer bordering upon the bark appeared under the mi- 

 croscope as having a width of half an inch, while the summer 

 layer of the previous annual ring had a width of one inch, he 

 took it for certain that the tree was cut in the middle of the sum- 

 mer period ; if, however, there were only a narrow layer of 

 summer cells under the bark, it would indicate to him that the 

 tree was cut in the early spring. Since, however, the width of 

 summer layers as well as winter layers varies not only in differ- 

 ent trees, but even in the same tree from year to year, it is not 

 enough to compare the width of the last wood with the width of 

 the corresponding layer of the previous year only. In order to 

 obtain accurate results, it is necessary to compare the width of 

 the last wood with the average width of a layer of the same char- 

 acter for a number of preceding years. 



In determining the time of cutting of old trees, and especially 

 of trees that have been lying for a long time on the ground, it 

 often happens that it is difficult to make out the cells under the 

 microscope, and therefore to determine the time of cutting. In 

 such case it is well to dip the section of wood into a solution of 

 iodine which colors the walls of the cells a dark orange and en- 

 ables them to be more readily distinguished. 



The results of these investigations are fully illustrated by a num- 

 ber of photographs of the structure of the last wood as it appeared 

 under the microscope. 



Since the exact date of cutting of the tree from which each sec- 

 tion has been taken is definitely known, these photographs obtained 

 by means of a microscopic camera afford a most interesting in- 

 sight into the development of the layer of wood during the entire 

 year. 



These investigations convinced Rashevsky of the entire accur- 

 acy and practicability of such a method of determining the time 

 of cutting to such an extent that it was made compulsory by the 

 railroad for which he worked for all the inspectors to make mi- 

 croscopic examinations of not less than four samples from each 

 consignment of ties. If among these samples even one proved 

 of summer cut, the whole consignment was rejected and had 

 to be removed from the railroad grounds and substituted by 

 another consignment of ties of winter cut. 



In order to make these examinations, it is not necessary of 

 course, to go to the same length as did Rashevsky in his pains- 



