NO. I GROWTH LAYERS IN TREE BRANCHES — CLOCK ET AL. 163 



complete, entire growth layer free of compression wood. The mostly- 

 sharp lens covers an arc of 270°. At its widest part, the densewood of 

 the lens is divided into two sharply bordered bands which actually are 

 transitional between divided densewood and a short, sharp lens. 



ip3S, at 107 cm. — The inner sharp, complete, entire growth layer 

 makes up most of the increment. Traced around the circuit the two 

 sharp, complete, entire growth layers vary in relative thicknesses. At 

 89 cm. — The inner sharp, complete, entire growth layer contains an 

 exterior lens of 200° whose densewood, near one cusp of the lens, 

 divides into three bands making doubly divided densewood. These 

 are resolved only under high power. However, the cells of the outer 

 band of densewood grade tangentially into wider and wider cells 

 until there is a complete transition from divided densewood of the 

 inner growth layer to a sharp half-lens within the interior of the 

 outer growth layer. The outer growth layer itself also contains di- 

 vided densewood. 



ipj4, at 107 cm. — Increments for 1934 and 1935 are separated with 

 difficulty. Actually there are five to eight growth layers in the two 

 years. On the short radius, 1934 is single. The long radius contains 

 a decided bulge made up of several diffuse lenses. Thus cambial ac- 

 tivity, locally rapid, is decidedly rhythmic. Many bulges among our 

 specimen branches are built up by series of half-lenses facing each 

 other. Careful search with high power shows that the densewood of 

 the half -lenses in many cases can be traced tangentially across the 

 bulge to their counterparts on the other side. The narrowness and 

 sharpness of the lenses at and near their cusps suggest not so much 

 differential cambial activity within the active area as the completeness 

 and duration of cambial inactivity and maturation processes which 

 become progressively less when traced from cusp point inward tan- 

 gentially to mid-lens. 



ip3j, at 107 cm. — Each of the sharp, complete, entire growth lay- 

 ers contains a long, sharp, exterior lens. In contrast with 1932, as 

 well as with numerous examples in other branches and trees, the 

 outer sharp, complete, entire growth layer makes up the main bulk 

 of the 1935 increment. At 89 cm. — The increment for 1935 is set 

 off from that of 1934 chiefly on a color basis — the separation is 

 necessarily uncertain because 1935 can have no frost and because of 

 multiple sharp, complete, entire growth layers in both years. It is set 

 off from 1936 by typical frost injury at the start of 1936. On the 

 long radius, the inner sharp, complete, entire growth layer has a sud- 

 den bulge, part of which is due to a 120° exterior lens. Just outside 

 this lens the middle sharp, complete, entire growth layer contains an 



