Periodical Literature 325 



of the injury is less noticeable eastward and is not apparent east 

 of the crest of the Cascades. The author suggests "parch blight" 

 as an expressive and distinguishing name for this injury. 



C. D. H. 



Parch Blight on Douglas Fir in the Pacific Northwest. The Plant World, 

 February, 1916, pp. 46-7. 



Curiously enough, the explanations of the 

 How commonplace phenomenon of diameter 



Trees Grow growth are still quite fragmentary and 

 in usually the formation of the annual ring 



Size is merely declared an "inherited character- 



istic." Dr. Jaccard discusses the matter in 

 detail under three headings, namely, the change in anatomical 

 composition of wood during the season ; the periodic formation of 

 annual rings under influence of exterior factors ; the form 

 acquired as a result of annual ring formation and their varying 

 width. 



The formation of the early or spring wood zone, with many 

 vessels of large lumen, is ascribed to the need of increased trans- 

 portation of water and nutrients upon the formation of foliage. 

 The flattening of the later woodcells is not so easily explained. 

 De Vries could produce flat cells in spring wood by applying 

 a rigid bandage around the bark, and spring wood in the sum- 

 mer by properly located incisions in the bark, from which he 

 deduced the change of spring and summer wood to bark pressure, 

 which growing in the summer is by the splitting of the bark re- 

 leased in winter. 



This Sachs-de Vries theory, however, does not explain the sud- 

 denness of change from spring to summer wood. Russow ad- 

 duced change of osmotic pressure in the cambium cells at different 

 seasons, but Wieler's attempts to measure these pressures did 

 not substantiate the theory. The author suggests that Wieler's 

 series was too small to permit generalization, and Krabbe has 

 shown that this pressure does not vary very much through the 

 year; the bark expands with formation of the ring, hence does 

 not explain the phenomenon. The reduction in lumen of summer 

 wood cells is often accompanied with thickening of the cell walls : 



