STUDIES IN PLANT RESPIRATION AND PHOTOSYNTHESIS. 31 



to the preparation of amino-acids. The laboratory at Carmel, 

 California, had not yet been completed, and we are greatly indebted 

 to Professor G. N. Lewis for extending to us the opportunity of 

 carrying out a large part of this preparation work in the chemical 

 laboratories of the University of California. We were thus enabled 

 to prepare adequate quantities of a variety of amino-acids of the 

 highest purity. 



The mineral nutrient solution, recommended by Dr. B. M. Duggar, 

 was the following: Solution No. 1: 3 grams CaS04 in 3,000 c. c. 

 HaO. Solution No. 2: 6 grams MgS047H20 in 1,000 c. c. H2O. 

 Solution No. 3: 3 grams Merck's ''soluble ferric phosphate" in 

 1,000 c. c. H2O. Solution No. 4: 12 grams KCl in 1,000 c. c. H2O. 

 The complete nutrient solution was made by mixing in the following 

 proportions: 30 c. c. No. 1; 10 c. c. No. 2; 10 c. c. No. 4; diluted to 200 

 c. c. ; and then 40 c. c. of No. 3 was added. This mixture gave excellent 

 results. A number of other commonly used nutrient solutions 

 employed in the preliminary experiments were unsatisfactory 

 because the leaves, after being in the dark for some time, were 

 wilted at the tips, had dark spots, appeared rather yellow, or showed 

 other abnormal conditions. 



All the solutions were thoroughly sterilized before using by twice 

 heating in the autoclave to 15 pounds pressure. The mineral 

 nutrient, sugar, and amino-acid solutions were heated separately 

 before mixing. The dish and the glass tubes which held the leaf 

 petioles were also sterilized. 



Great care was exercised in selecting the leaves in order to use 

 those of the same age and development. Consideration was also 

 given to the conditions to which the plants had been exposed previous 

 to the cutting of the leaves, viz, temperature and illumination. 

 Where this was of importance the leaves were taken only when these 

 conditions were as nearly the same as can be obtained in a green- 

 house. The petioles of the leaves were cut under distilled water. 

 They were immediately taken to the laboratory and about an inch 

 of the petiole cut off under water. In the meantime the nutrient 

 solution had been prepared and placed in the respiration chamber. 

 The leaves were then quickly transferred to the solution in the 

 chamber, care being taken that a drop of water adhered to the end 

 of the petiole. The leaves were placed as loosely as possible, with 

 the petioles well submerged in the nutrient solution. The glass 

 cover was then placed over the chamber and then the metal cover. 

 The level of the water in the thermostat was raised so that it covered 

 the entire chamber. Before cutting the leaves the absorption tubes 

 had been filled and connected, so that as soon as the chamber was 

 closed the air-stream could be started through the apparatus. For 

 about the first hour no account was kept of the carbon-dioxid emis- 



