093 .TOURNAI, OF FORIiSTRV 



Quality 1 culminates at 50 years with a yield of 135 cubic feet per acre. 



Quality II culminates at 55 years with a yield of 118 cubic feet per acre. 



Quality III culminates at 55 years with a yield of 99 cubic feet per acre. 



Quality IV culminates at 65 years with a yield of 82 cubic feet per acre. 



Quality V culminates at 70 j^ears with a yield of 6,3 cubic feet per acre. 



This indicates that the average culmination of mean annual incre- 

 ment of planted spruce in Britain is about 60 years and that this would, 

 accordingly, constitute the economic rotation. 



The authors of this bulletin, Messrs. Guillebaud, Steven, and Mars- 

 den, are to be congratulated on this substantial addition to the forestry 

 literature, not only of the United Kingdom, but of the entire world. 



A. B. R. 



Grozvth in Trees. By D. T. MacDoitgal. Carnegie Institution of 

 Washington, Publ. 307, 1921. 



MacDougal's studies on the growth of trees by means of his den- 

 drograph have already brought out interesting facts and show promise 

 of others. The dendrograph gives on a revolving drum a continuous 

 record of the minutest variations m the diameter of the tree. The 

 essentials of the instrument are a frame of metal placed around the 

 trunk to hold the contact points, and resting on a belt of wooden 

 blocks : the variation in distance between a contact rod on one side of 

 the trunk and of one end of a rod or lever on the oppsite side is traced 

 by a pen on a recording cylinder. The instrument can be adjusted so 

 that the record shows the variation of the trunk amplified as much as 

 is desired up to certain, limits, amplifications of from 5 to 25 times 

 being used by MacDougal. 



The trees studied include 15 species, among which are western 

 yellow pine, Douglas fir, Monterey pine, California live oak, and beech 

 in Maryland. It would seem that each species has its particular man- 

 ner of growth. 



The records show that increase in diameter is not continuous during 

 the growing season, nor is the trunk of a tree stationary in size when 

 it is not growing. There is a diurnal expansion and contraction, 

 greater in some species than in others ; small in California live oak, 

 and large in the pines, Douglas fir, and spruce, but particularly large 

 in Arizona ash. The minimum size occurs in the daytime, and maxi- 

 mum at night, showing that this variation is a moisture, not a tem- 

 perature response. Growth is superposed on these diurnal variations. 



