236 Prof. J. B. Farmer. On the Quantitative Differences in the 



Table II. — Twenty-seven Birch Twigs. Leading (or Terminal) Shoots. 



Age in 

 years. 



A ypfi m 7 TIP IIP a I v 1 Ol 



XJLl COi IXi XilKjUKm I A X\JJt 



Absolute vol. of water 

 passed in ^ hour. 



Specific vol. of 

 water per i hour. 



1 



2-46 



7-6 



48-0 



1 



2-26 



7-2 



49 -0 



1 



2-30 



7-2 



48-5 



1 



1-95 



8-4 



67 -0 



1 



3-18 



13-0 



67 -0 



1 



2-25 



5-4 



37 -0 



1 



3-33 



11 -2 



53 -5 



1 



3-00 



12 -3 



65-0 



1 



2-60 



7-7 



45-5 



• 1 



2-03 



5-5 



42 -5 



1 



3-98 



8-2 



32 -0 





2-65 



7 -0 



41 -0 



1 



2-16 



6-0 



43 



1 



1-34 



3-0 



34 -7 



1 



2-46 



6-5 



41 -0 



1 



2-09 



4-4 



32 -5 



; 



1 -75 



4-6 



40-7 





2-46 



6-2 



39 -0 





2 -29 



6-6 



44 -5 





1-88 



6-1 



50 -0 





1 -96 



6-0 



55 -0 



j 



2-58 



8-4 



50 -0 





2-36 



8-0 



53 -0 





1 -81 



4-2 



36-0 





X yo 



8 D 



ft*? »f\ 



Ol U 





2-33 



5-4 



36 -0 



2 



2-32 



5-8 



39 -0 





63 -76 sq. in. (at x 10) 

 =4 '12 sq. cm. (actual size) 



190 -5 



190-5 -46 •2 .. 

 4 -12 



1257 -9 

 Average = 46 •6... 



With the results obtained from these young trees it is useful to compare 

 those taken from branches cut from a tree of 14 years of age, and about 

 22 feet in height, felled in July, 1917. 



The mean value of the position of greatest density of the numerical results 

 both fall somewhat below that of the young laterals, but above that for the 

 young terminal shoots. 



The main average range for the Birch extends from about 38 to 58, with 

 very distinct maximal densities round 42 and 52. This result was arrived at 

 as the result of investigating 164 stems chosen at random. The annexed 

 figure, in which these are shown plotted on squared paper, shows that it is 

 hopeless to expect to get any single significant average. It will be noted that 

 there is a small but fairly well-defined group about 63. These exceptionally 

 high numbers may occur in twigs of any age and any diameter. They are 

 more frequent in the Birch than in most other species examined by me, but 

 they occur occasionally in most deciduous trees. 



