Senile Changes in Leaves of Certain Plants 



297 



affect the size of the islets. This was investigated by collecting various 

 leaves from vines of approximately the same age, the variation being a 

 few years, and determining the weight per 100 square milhmeters of leaf 

 blade of each leaf and the size of the vein islets of each. The difference 

 in weight is taken to mean differences in thickness, as all the leaves were 

 picked at the same time of day. The data obtained are given in table 3: 



TABLE 3. Area of Vein Islets in Leaves of Different Thicknesses 



Number of leaf 



Weight of 



100 square 



millimeters 



of leaf 



(grams) 



Area of 



(islets 



square 



miUimeters) 



1 



0.83 

 0.87 

 0.89 

 0.91 

 0.99 

 1 04 

 1.16 

 1.20 

 1.36 

 1.43 

 1.51 

 1.61 

 1.63 

 1.67 

 1.69 



0.3597 



2 



0.3669 



3 



0.3663 



4 ' 



0.3207 



5 



0.3818 



6 



0.3777 



7 



0.3263 



8 



0.3197 



9 



3217 



10 



0.3696 



11 



0.3612 



12 



3667 



13 



3580 



14 



3716 



15 



3691 







Influence of such differences in light as are found in nature on the size of 



vein islets 



Schuster found that the effect of light on the veins was not the same in 

 all plants. The leaves of some plants showed an increased amount of 

 venation (smaller vein islets) when grown in the shade, others were not 

 affected, and still others showed a decrease. One of the plants investi- 

 gated by Schuster was Ampelopsis veitchii, a genus of the Vitaceae, and 

 this showed, if anything, a tendency to decrease in amount of venation 

 in strong light (resulting in increase in size of vein islets). The same 

 tendency was found to be true in Vitis vulpina to a slight degree (table 4). 



