KNUDSON: CAMBIUM DEVELOPMENT IN AMERICAN LARCH 293 



results obtained by Whitten* on the date of blossoming of green- 

 and purple-twigged peach trees. 



The temperature of the soil moisture and of the air, and the 

 thickness and color of the bark are not the only factors operative 

 in inducing diameter increase. Certainly as regards all of the 

 above factors the branches are all more favored than the trunk 

 of the tree, yet in the isolated tree E the diameter increase began 

 first in the trunk. Food supply may be a factor in stimulating the 

 cambium of the trunk to diameter increase, before there is develop- 

 ment in the branches. It is not possible to state the influence of 

 food supply. Controlled experimental work with this as well as 

 with the other factors is necessary to give an idea of the influence 

 of each in stimulating the cambium to activity. 



In conclusion it should be stated that considerably more work 

 is necessary in order to establish the region of the tree in which 

 cambium activity first begins. No doubt different conditions will 

 be found for trees of the same species of different ages, and for 

 trees of different species and genera. Investigations of this 

 character are important because only by such studies can the 

 factors be determined which stimulate cambium activity. It is 

 essential also to determine the period and extent of phloem and 

 xylem formation in trees and the duration of cambium activity. 

 Much more work remains to be done along this line. Such work 

 is of especial importance in fruit culture and in a subsequent paper 

 the results of such an investigation will be presented. 



CORNELL UNIVERSITY. 



Explanation of figures 



FIG. i. Cutting no. 6 made from trunk on November 13, showing cambium 

 tissue a to a, consisting of six rows of cells; X475. 



FIG. 2. Shows extent of cambium in basal cutting, No. 10, made on May 5. 

 Compare with Fig. 2; X475- 



FIG. 3. Cutting no. 6 taken from trunk of tree A on May 5. Cambium a to a. 

 Note the increased diameter and cell differentiation; X475- 



FIG. 4. Cutting no. 5 made on May 25 from tree A. Xylem formation not yet 

 begun; X33- 



FIG. 5. Cutting no. 4 from tree C made on June 3; X33. 



FIG. 6. Cutting no. 7 from tree C made on June 30; X33. 



FIG. 7. Cutting no. 8 from tree C made on July 8. Differentiation of summer 

 wood is beginning; X33- 



* Whitten, J. C., loc. cit. 



