Plate i 



Fig. I. CMP i-i-b. Branch section of Piiius ccmbroidcs. cut January 3, 1941. 

 Xylem probably of 1937-1940. Normally developed growth layers in a pine; 

 probable natural frost injuries in 1938 and 1940; incipient visible growth 

 rhythm and initial departure from unity in 1940. Compare with plate 3, 

 figure 2. 

 Fig. 2. CMJ i-i-a. Branch section of Junipcnis pachyphloca, cut January 3, 1941. 

 Xylem of 1937-1940. Intimate relation between frost injury of 1938 and dw* ; 

 bifurcation of annual densewoods and contrast of outer densewoods of an- 

 nual increments. 

 1937: multiple dw ; see. 

 1938: msce connected with frost injury, dw filling gaps in discontinuous 



circle of injury and following outward the injury effects themselves ; 



msce whose dw spreads into a curtain efl^ect giving diffuseness, then 



changes to sL. 

 1939 : 2 see, outer dw with ddw which changes tangentially to sL. 

 1940 : see. 



* For explanation of abbreviations, see page loi. 



