Determining Time Timber Was Cut. 409 



taking work by means of costly instruments. Such instruments 

 are, of course, necessary for careful scientific investigations, but 

 for ordinary determinations of the time of cutting, a cheap 

 microscope with a magnifying power of 140, which can be bought 

 for $25 or $30, a sharp penknife and a small piece of wood con- 

 taining a portion of the last layer of wood are about all that is 

 needed for such examinations. 



Rashevsky's examinations, supported by microscopic photo- 

 graphs of the actual structure of the wood obtained from trees 

 cut each month of the year, open also a new field of investigation 

 into the structural changes which take place in the annual layer 

 after the close of the vegetative period. 



Rashevsky's studies do not leave any doubt as to the possibility 

 of determining from the appearance of the last wood layer 

 whether the tree was cut in the spring, summer, or during the 

 dormant period of the tree. This for the practical end which is 

 sought by such a method is all that is required. His claim, how- 

 ever, to be able to tell from the appearance of the last layer 

 whether the tree was cut in the late fall or middle winter, must 

 be taken with considerable reservation. It is evident that there 

 can be no increase in the width of the last layer after the growing 

 season is over. The actual division of the cambium cells and the 

 formation of wood elements take place within a comparatively 

 short time, in the temperate climate between May and July. 

 While the new layer of wood is in the process of growth its 

 width may serve as a measure of time; but after its growth is 

 completed it is hard to see how the width of its winter wood can 

 determine whether the tree was cut in the beginning or the middle 

 of winter, unless some subsequent changes take place in the zvood 

 elements, which change the proportion of summer and winter 

 wood in the annual layer. This would open new vistas into a 

 field which so far has been but little investigated. 



[The Editor can not allow this contribution to pass without accentuat- 

 ing and enforcing Mr. Zon's doubts as to the likelihood of structural 

 changes in the wood during winter. 



It is well established, we think, that different species in the northern 

 climate exhibit growth periods of different lengths (some extending it 

 into September, see Quarterly, Vol. V, p. 259), but also, that all cease 

 growing in winter. The Russian Civil Engineer evidently knew little of 

 the physiology of tree growth, and his scheme sounds fanciful. All he 

 could possibly determine is whether the wood was cut before or after the 

 summer wood of the year had been formed. — Ed.] 



