1262 AGRICULTURAI, BOTANY, CHEMISTRY AND THYSIOLOGY OF PI^ANTS 



variation in the network of veins on the leaves is a progressive modifica- 

 tion in the cells of the meristeni and the leaf inherent in the nature of their 

 protoplasm, this progressive variation being called senility in regard to ani- 

 mal protoplasm ; the increase of the vascular tissue of the leaf with age 

 furthermore constitutes a degeneration as regards physiological activity. 

 In order to establish this latter point the writer compared the photo- 

 synthetic activity of leaves belonging to old or young trees respectively. 

 He made use of a method of approximation consisting in determining the 

 gain of weight in one day of fragments of leaf equally exposed to sunlight. 

 The determinations, carried out in August, gave the following general 

 results as regards Vitis vulpina : 



Average gain for leaves of 5 to 8 year old vines 0-4 % by weight 



Average gain for leaves of 20 to 25 j^ear old vines 1.4 % " " 



He likewise determined the rate of elimination of carbonic acid in 

 leaves taken from Vitis vulpina at different ages, and obtained the total 

 results exhibited by the following table : 



Average age of the young vines utilised 7-3 years 



Average age of the old vines utilised 25.4 years 



Number of determinations made 92 



Average duration of each determination 23.86 hours 



Rate of elimination of carbonic acid for the young vines . 0.0349 % per hour 



Rate of elimination of carbonic acid for the old vines . 0.0297 % per hour 



He next started to determine the quantity of water absorbed by 

 young and old vine leaves, reduced to fine powder, in order to have indi- 

 cations as to the capacity of living leaves to retain water. He observed 

 first of all that acidity is higher in the powder of young leaves than in that 

 of old leaves (in the former case an average of 2.2 cc. of a decinormal solu- 

 tion of potash is required to neutraHse 0.2 g. of powder, against 1.5 cc. for 

 old leaves) ; in order to get rid of the influence of this acidity, he neutra- 

 lised the substances subjected to experiment and obtained the following 

 results : 



(General average of water absorbed by the leaves of Vdung vines .... 489.0",, 



(General average of water absorbed by the leaves of old vines 387.9 "0 



Finally, he looked for and found other signs of senihty. Thus he ob- 

 served the variations in the number of stomata in Vitis vulpina of dif- 

 ferent ages. 



Nwiibcy ()/ sivmala in 1 sij. mm., aveyagc joy vines oj : 



5 to 7 years 117 



8 to 10 years 120 



20 to 30 years . 282 



He next proposed to determine the size of these stomata, and reached 

 the following results : 



