Senile Changes in Leaves of Certain Plants 333 



The vines with 20 and 40 rings, used in the second experiment, are 



not included in the following summary, as both belong to the same class 



and no results from young vines on the same day were obtained from 



vines adjacent to them: 



Average gain for leaves of vines with from 5 to 8 rings 9.4 per cent gain in weight 



Average gain for leaves of vines with from 20 to 25 rings .... 1.4 per cent gain in weight 



A comparison between the carbohydrate-producing power of leaves 

 in different stages of development on vines of Vitis vulpina gave the 

 following results: 



Average gain for leaves from 2.5 centimeters long to mature, 6 rings 13.3 per cent 



Average gain for leaves from 2.5 centimeters long to mature, 15 rings 9.2 per cent 



A comparison between leaves of Ampelopsis veitchii eight years old 

 and nineteen years old, growing on a south wall with as nearly identical 

 hght exposure as could be obtained by any means, gave average results 

 as follows: 



Average gain for leaves of vine eight years old . 15 . 1 per cent 



Average gain for leaves of vine nineteen years old 9.7 per cent 



conclusions regarding relative rate of carbohydrate production 

 IN the leaves of young and of old vines of vitis vulpina 



AND AMPELOPSIS VEITCHII 



While the difficulty of obtaining leaves with identical hght relations 

 on adjacent vines of different ages limited the experiments to but few 

 in number, the unvarying result of the tests is strong evidence in support 

 of the statement made above, that senile deterioration is occurring in 

 the leaves of perennials. It is not probable that translocation is more 

 rapid in the leaves of old plants than in those of young plants. The 

 number of large veins is not increased, and the increase in number of 

 veinlets probably only keeps pace with a decrease in the rate at which 

 materials can diffuse through the cells of the leaf, as will be explained 

 subsequently. 



RATE OF ELIMINATION OF CARBON DIOXIDE IN PICKED LEAVES OF 

 VITIS VULPINA OF DIFFERENT AGES 



It seemed possible that a comparison of the rate at which carbon dioxide 

 is eUminated from the leaves of old and of young vines would give some 



