Fig. 17.—XSC i-2-b. Increments for 1938-1939. Partial gls ; variable long radius. Interpre- 

 tion shown in figure 18. 1938: Effects of natural frost; see; msL; sL; 1939: effects of 

 itural frost; s -jL; see; sL. 



{-2-h 



Fig. 18.— An interpretation of figure 17. Localized and periodic activity of growth processes, 

 f contacts between gls are classified as sharp, diffuse, or "invisible," gl patterns are simplified 

 nd periods of activity (or flushes) are clarified. Gls are numbered i to 6 to correspond to 

 eriods of growth activity. If the contact between 4 and 5 is interpreted as partly invisible 

 blank space, 42-51), then 4 becomes an entire gl and 5 an ordinary lens. 



Interpretation of a contact as invisible suggests that growth activities can cease without wall 

 hickening, heavy lignification, and failure to enlarge among the last formed cells. Lightwood 

 5 continuous across an invisible contact. By recognizing such a contact, half-lenses and arcs 

 lecome understandable both physiologically and anatomically. 



75 



