334 Harris M. Benedict 



evidence of the relative katabolic activity of the two stages. Since 

 as near the normal respiration as is possible in detached leaves was desired, 

 care was taken not to subject the leaves to other disturbing conditions. 

 The method was as follows: Ten healthy, mature leaves of each vine 

 to be studied were picked and were taken at once to the laboratory. Here 

 they were carefully wiped clean of dust with a soft, dry cloth, the petioles 

 were cut off at the base of the blades, and the blades were weighed. Each 

 set of ten leaves was then placed in an air-tight respiration chamber. 

 The respiration chamber, a 4-liter bottle, was supplied with air which 

 had been drawn in turn through a gas-washing bottle employed as a 

 safety and through a gas-washing bottle filled with a concentrated solution 

 of potassium hydrate. The air leaving the respiration ■ chamber was 

 passed through a calcium-chloride tower for the purpose of removing 

 its water vapor, then through a potash bulb, then through another calcium- 

 chloride tower, and finally through another safety. The air current 

 was provided by means of an aspirator with a regulated outflow. 



Eight series of this type were set up side by side in such a way that 

 temperature conditions were the same for all. Tests of old and of 

 young leaves were run simultaneously, and frequent blanks in the 

 different series were employed as checks. The leaves were so arranged 

 in the containers as to prevent their packing together and thus possibly 

 giving rise to such heat production as Mohsch (1908) describes. The 

 containers were covered with black paper. The experiments were 

 brought to a close as soon as any indication of injury to the leaves 

 appeared. 



In tables 47 to 51 the percentage given in the last column is based 

 on the green weight of the leaf and the weight of the carbon dioxide col- 

 lected in the potash bulbs and reduced to the average per hour for the 

 entire time of the test. It represents, therefore, the hourly percentage 

 of carbon dioxide eliminated from the green leaves. This rate will be 

 lower than if the dry weight of the leaves could have been used. Since 

 this could not be obtained before the experiment, and the leaves at the 

 end of the test had undergone respiratory losses, the use of the green 

 weight as the basis of calculation was necessary. The leaves from the 

 younger vines contain a greater percentage of water than do those from 



