332 CARNEGIE INSTITUTION OF WASHINGTON. 



and thus serves to correlate the two series. The standard plants used 

 were wheat, oats, sunflower, and bean. These all gave good results 

 with the exception of oats, which was unsatisfactory in most of the 

 stations, probably owing to the variety selected. The sunflower and 

 bean were especially valuable, due chiefly to the fact that they are 

 widely different in their transpiration and photosynthetic activity. In 

 all the stations weekly weighings were made of the plants and they 

 were consequently maintained in practically the same w^ater-content 

 throughout the period. Some attention was paid to the effect of the 

 size of the container, and it was found that, while larger containers 

 promoted better development, smaller ones were more convenient and 

 lent themselves to a wider range of conditions, particularly in the 

 mountains. It was found necessary to conduct a special series of 

 experiments to test the seals used in the phytometers. The usual wax 

 seals were found to be quite unsatisfactory for field use because of the 

 extreme conditions to be met. Wax sufficiently soft to prevent crack- 

 ing will not remain solid under the extreme noon-day temperatures, 

 especially in gravel-slides. In the hope of findilig a wax seal which 

 would be satisfactory under a wide range of conditions, various com- 

 binations of paraffin, beeswax, and petrolatum were tried, in addition 

 to grafting-wax and collodion. The most effective method found was 

 to coat burlap covers, stretched smoothly over the containers, with a 

 wax composed of 5 per cent of beeswax, 5 per cent of petrolatmn, and 

 90 per cent 54° paraffin. When in a semi-liquid condition, the capillary 

 attraction of the burlap fibers serves to prevent the seal from running, 

 while the loose weave of the cloth allows monocotyls to come through 

 as readily as the wax alone. 



Photosynthetic Efficiency, hy F. E. Clements and Frances Long. 



In the endeavor to measure the carbohydrate production of plants 

 in the field and to correlate it with light intensity and water use, 

 further studies have been made in habitats with measured light con- 

 ditions. These have dealt chiefly with the two major lines of last 

 year, namely, the photosynthetic activity of different species in the 

 same light value and of the same species under different light inten- 

 sities. The latter appears to exhibit basic correlations with the definite 

 adaptations shown in shade ecads. The efficiency of the leaf at differ- 

 ent levels and at different positions in the crowns of trees and shrubs 

 has also received considerable attention. Standard plants in the 

 climax and serai phytometer series have been studied with reference 

 to differences in photosynthetic efficiency at various elevations. It is 

 thought possible that plants may respond to differences in total light 

 intensity that can not be recognized by photometric methods. It is 

 also expected that a more or less definite correlation between photo- 

 synthate, transpiration, and dry weight may be discovered in the case 



