312 



Harris M. Benedict 



0.6C 



p 



I O.oO. 

 '^ I 0.40 

 .S3 0.30 



> - 

 'S 0.20. 



CO 



0.10 



50 



60 70 



Fig. 55.— 

 size of 



10 20 30 40 

 Age in years 



- Curve showing decrease with age in 

 vein islets of leaves of Vitis vulpina 



By averaging the size of the vein 

 islets in vines of the same age, a 

 curve can be plotted which shows 

 very strikingly' the decrease in the 

 size of the islets with increasing age. 

 Such a curve is shown in figure 55. 



When the plants in the above 

 summary are divided into groups 

 the change in venation is even more 

 apparent, as shown in table 22. 



In figure 56 are shown photo- 

 graphs of the venation character- 

 istic of each of these groups. 



TABLE 22. Average Area of Vein Islets in Leaves of Vines Grouped According 



TO Age 



Number of rings ... 



3 to 5 



6 to 11 



14 to 25 



28 to 35 



50 to 70 







Area of vein islets (square millimetei's) 



0.4941 



0.3727 



0.2969 



0.2211 



. 1638 



3 6 U 



Age in years 

 Fig. 56. — Photographs of vein islets of leaves of Vitis vulpina vines of the ages of 3, 6, 

 IJj., 28, and 60 years, grown under ideyitical conditions 



Size of islets in leaves of cuttings grown under identical conditions 

 In order to test further the constancy of the different sizes of vein 

 islets found, cuttings were made, in three different summers, from the 



