330 CARNEGIE INSTITUTION OF WASHINGTON. 



Several instances of apparent activation of enzymic hydrolysis of 

 starch by amino acids have been recorded by previous workers, but by 

 other investigators have been attributed to the influence of the added 

 substance upon the reaction of the digestion mixtures. In our experi- 

 ments it was demonstrated by the electrometric method that the 

 activating effect of neutralized aspartic acid, or asparagin, was not due 

 to change of hydrogen-ion concentration. Neither is it referable to the 

 sodium ion nor to the mere concentration of electrolyte, since optimum 

 concentrations of chlorides and phosphates were already present. The 

 activating effect of the neutralized amino acid upon the enzyme appears 

 to be specific in the sense that sodium aspartate (for example) increases 

 the enzymic activity when the optimum amounts of chloride and phos- 

 phate are already present, while the aspartate can not completely 

 replace the chloride in the activation of pancreatic amylase. The 

 experiments are being extended to the study of the effects of other 

 amino acids upon the different amylases. 



The efficient work of those who have collaborated in these investi- 

 gations, whether as research assistants or volunteers, is gratefully 

 acknowledged. 



ECOLOGY. 



Clements, F. E., Tucson, Arizona. Associate in Ecology. (For previous 

 reports see Year Books Nos. 16 and 17.) 



The experimental work of the year has practically all been done at 

 the Alpine Laboratory from June to September. The chemical deter- 

 mination of the degree of photosynthetic activity and of the presence 

 and amount of rubber in a wide range of plants has been carried on at 

 the Desert Laboratory at Tucson during the winter. Vegetation 

 studies have been made throughout the year. During the winter these 

 have dealt chiefly with the desert scrub and desert plains within a 

 radius of 75 miles of Tucson. Through the summer they have been 

 concerned with the mixed prairie and chaparral of the plains and foot- 

 hills about Colorado Springs. The ecological relations of roots have 

 been further investigated in Nebraska, Kansas, Colorado, and South 

 Dakota, and experimental quadrats for the study of vegetation and 

 crop ecology have been installed in Nebraska and Colorado. 



Two field expeditions have again covered the major portion of the 

 West. The first visited eastern Arizona, New Mexico, and eastern 

 Colorado during May and June; the second traversed Colorado, 

 Wyoming, Utah, Idaho, Oregon, California, and Arizona in September 

 and October. A large number of problems were touched more or less 

 thoroughly, chief among them being cooperative grazing research, 

 climax formations, permanent quadrats, basic changes in grassland, 

 variation of genera such as Artemisia and Chrysothamnus, and native 

 rubber plants. 



