H. S. REED 



555 



cultivation, etc. Nevertheless the Juglans regia trees grew 42 days 

 later than the Juglans nigra trees. It is well known that there is a 

 great difference between these species in respect to distribution and 

 resistance to cold weather. Juglans regia is reported to be a native 

 of Persia, the Himalayas, and China, while Juglans nigra is a native 

 of the eastern United States. The remarkable fact, as far as these 

 250 



200 



150 





100 



50 



55 



80 



155 



180 



105 130 



Time in. days 



Fig. 4. Growth rate of Juglans regia trees. The curve represents the values 



oc 

 obtained from the equation log TT:rz — =K (/— 96); points within circles rep re- 



sent the observed mean height at various intervals. 



notes are concerned, is that Juglans nigra trees went into a condition 

 of dormancy early in September, while Juglans regia trees, growing in 

 adjoining rows and with similar care, grew until the middle of 

 October. 



This observation sustains the conclusion drawn from the foregoing 

 studies on the rate of growth, and indicates that the extent of the 

 growth cycle as well as the amount of growth is controlled by inter- 

 nal genetic factors. 



