Fig. 13. — XSC i-i-b. Increments for 1938-1940. Lansing. Interpretation shown in figxu 

 14. 1938 : Effects of natural frost ; dee ; see ; 1939 : iL ; msce ; sL ; ^L ; sL overlappir 

 previous sL; 1940: effects of natural frost; see. 



XSCI-l-b 



Fig. 14. — An interpretation of figure 13. Localized and periodic activity of grow 

 processes. Contacts sharp, diffuse, or invisible. Dw at first sharp, then diffuse, then no 

 existent as an "invisible" contact (long blank space) ; hence, half-lenses become actual lens< 



Letters ^ to £ give successive episodes of cambial activity. Dw of A becomes diffuse 

 Ax and disappears to the left where the blank space represents an invisible contact, i.e., no d 

 developed. C overlaps B, D overlaps C, and E and D are a compound lens. Dw of D fai 

 at D\ and an invisible contact is pictured as continuing the dw (half-lens) in order to produ 

 a relatively simple lens. Such interpretation simplifies the picture of cambial activity, cambi 

 inactivity, and maturation, or lack thereof, of dw cells. 



72 



