Senile Changes in Leaves of Certain Plants 



295 



tance. The writer's measurements with Vitis vulpina also indicate that 

 the size of the leaf has comparatively httle effect. Tlie figures in table 1 

 may be considered as typical: 



TABLE 1. Area of Vein Islets in Leaves of Different Sizes on the Same Plant. 



Vine 29 



Number of leaf 



Breadth 

 of leaf 

 (centi- 

 meters) 



Length 

 of leaf 

 (centi- 

 meters) 



Area of 



leaf 

 (square 



centi- 

 meters) 



Area of 

 vein islets 

 (square 

 milli- 

 meters) 



1 



2 



3 



4 



11 

 17 

 12 

 11 

 13 

 14 

 13 

 15 

 17 

 14 



14 

 16 

 12 

 11 

 13 

 14 

 15 

 17 

 21 

 15 



108 

 190 

 101 

 85 

 117 

 117 

 127 

 179 

 250 

 147 



0.3762 

 0.3663 

 0.3818 

 0.3597 



5 



0.3669 



6 



7 



0.3733 

 0.3681 



8 



0.3703 



9 



10 



0.3777 



0.3784 







0.4C' 



0.30- 



It seems at first thought so natural to suppose that the size of vein 

 islets would be larger in the larger leaves, that a series of leaves was 

 collected from vines ranging in 

 age from seven to eleven years. 

 The size of each leaf and that 

 of its vein islets were measured, 

 and the results are presented in 

 table 2 and graphically repre- 

 sented in figure 54. 



It is evident, therefore, that 

 the formation of new veinlets 

 keeps pace with the expansion 

 of the leaf. A most striking ex- 

 ample repeatedly found in an- 

 other plant may be of interest here. Less than ten feet apart stood two 

 trees of Tilia americana, one three inches in diameter, the other fourteen 

 inches. The larger tree had been cut down, and from the stump were 



•|| 0.20' 



0.10 



75 100 125 150 175 200 225 250 

 Area of leaves in square centimeters 

 Fig. 54. — Curve shorving that size of leaf does not 

 determine size of vein islets 



