Plate 19 



Fig. I. TTP 34-s-b. Brancli section of Piiuts j^oiidcrosa. cut November 29, 1941. 



Xylem of 1937-1941. Atypical gls ; dated multiplicity; irregular margin. 



1937 : 2 see, each a typical gl. 



1938 : Zones of natural frost effects ; see partially indefinite. 



1939- gl nearly all dw ; msce ; at places appears to be merely ddw of 1938. 



1940; msce. 



1941 : Thin see, in places dw only (appears to be ddw of 1940) ; inc. gl with 

 irregular margin, drowth probably arrested on May 25, 1941, by 

 artificial freezing. 



Compare with plate 17, figures i and 2. 

 Fig. 2. TTP 24-14-0. Branch section of Piiiiis pondcrosa, cut January i, 1943. 



Xyleni of 1937- 1942. Typical 1938 frust injury and recovery in a pine; 



masking of sharp intra-annual by al)sence of Iw ; diffuse dw as initial de- 

 parture from unity. 



1937: Diffuse dw bands; see. 



1938 ; Complete circle of natural frost effects ; see. 



1939: see. 



1940; dee as example of initial departure from unity: see with heavy band 

 of dw which, by insertion of Iw near an injury, proves to be 2 see's. 



1941 ; see, with dw of variable width. 



1942; see. 



In 1940 increment, outer dw of the annual lies against dw of the intra-annual 



except near an apparent injury where Iw is inserted and 2 see's are thus 



revealed. Separation of the 2 see's can be followed under high power. See 



figure 3, below. 

 Fig. 3. TTP 24-14-0. Enlarged detail of figure 2, above. Xylem of 1940-1941. 



Apparent idw in center of dw band is actually at contact between 2 entire gls, 



outer one here reduced to dw only ; elsewhere on circuit, near an apparent 



injury, Iw is inserted and sharji character of 2 gls is revealed. See figure 2, 



above. 



