274 KNUDSON : CAMBIUM DEVELOPMENT OF AMERICAN LARCH 



north or south. Trees B, C, and D were very uniform as regards 

 size and form. Tree -A, although of the same age, was slightly 

 smaller. 



In order to determine the region of growth inception it was 

 necessary to take material from the apex of the tree to the base. 

 The larch has, at intervals, whorls of branches, the number of 

 which agree approximately with the age of the tree. The trees 

 used had each ten such whorls and material was removed from 

 below each whorl, at different times throughout the growing 

 season. Cuttings were made only from the south side of each tree. 

 The first cuttings were made a few inches below each whorl of 

 branches and the subsequent cuttings were made a few inches 

 below the preceding and a little to one side. In obtaining the 

 material for study two incisions, 2 cm. apart, were made through 

 the bark and into the wood to a depth of I cm. and the piece then 

 removed with a small knife. The injured area was then filled 

 with grafting wax. 



The material collected from trees A and B was fixed in a 

 solution consisting of 33 parts glycerine, 35 parts alcohol, 30 parts 

 distilled water, and 2 parts glacial acetic acid. The material 

 kept in this solution was in excellent condition for sectioning, 

 though, of course, no good fixing of the protoplasmic structure 

 was obtained. That collected from trees C and D was fixed in 

 Gilson's solution and kept, by mistake, in 95 per cent alcohol. 

 When attempts were made to section it, several months later, 

 considerable difficulty was experienced, because of brittleness. 

 Attempts to soften the material, by allowing it to remain in equal 

 parts of glycerine and alcohol, and also in glycerine alone, proved 

 futile. The greater part of the material was sectioned without 

 imbedding, but some of it was necessarily imbedded in celloidin. 

 The sections were cut from 20 to 40 JJL in thickness and stained with 

 safranin and Delafield's haematoxylin of the formula so commonly 

 used for wood staining, The methods employed during the 

 season of 1911 are described subsequently. 



INVESTIGATIONS OF 1909 



The first cuttings were made on April 19 and at this time 

 the buds located on the 4-, 5-, and 6-year old wood had opened, 



