306 CARNEGIE INSTITUTION OF WASHINGTON. 



Controlled field studies have been undertaken to determine whether the 

 percentage composition of the soil-air alters the rate of root absorption or the 

 amount of moisture remaining in the soil at the time of temporary or perma- 

 nent wilting and whether this varies markedly in plants typical of the prairie 

 formation. 



Physical Properties of the Sap of Engelmann Spruce, hy G. W. Goldsmith 



and J. H. C. Smith. 



Picea englemanni occurs from the base of the mountains to timberline in the 

 Pike's Peak region, although the best development is found near 9,000-feet 

 elevation. Since the time and rate of growth differ at the various elevations, 

 a study was undertaken of the sap expressed from the leaves. Temperatures 

 attainable by the use of salt-ice mixtures were not low enough to produce 

 permeability in the treated leaves, since comparable temperatures commonly 

 occur during the winter in the various habitats, and consequently treatment 

 with chloroform vapor for 48 hours at zero was employed to render the tissue 

 permeable. The sap-content, freezing-point, acidity, density, refractive 

 index, optical rotation, and titration curve were determined for each of four 

 samples of leaves taken from four stations, namely. Shelter Rock at about 

 7,000-feet elevation, Half Way at 9,000 feet, Timberline at about 12,500 feet, 

 and Krumholz at practically the latter elevation. The leaves were selected 

 from similar positions on the trees and were the youngest present in every 

 case, and hence they were never more than one year old. They were removed 

 from the twigs and immediately placed in the glass containers in which they 

 received the chloroform treatment. 



The sap-content of the leaves varied with the season and elevation, being 

 steadily reduced in the Krumholz during the winter, often reaching extreme 

 desiccation in March and April. During the same period the sap-content at 

 the other stations suffered a much smaller reduction. Desiccation was 

 accompanied by increased acidity. There was little optical rotation at any 

 period. The titration curves show a high buffer action at all seasons and 

 characteristic dissociation curves as the young leaves age and become 

 frost resistant. 



Experimental Pollination, hy F. E. Clements and Frances Long. 



During the present season the emphasis has been placed upon the relations 

 between nocturnal insects and flowers and upon constancy, especially at the 

 end of the season. Hyloicus separatus and Protoparce maculata were the usual 

 visitors for nectar to Anogra albicaulis and Pachylophus ccespitosus, and 

 frequently also to Gilia aggregata, a pink-flowered species, Sphecodes came 

 regularly at dusk and collected pollen alone, working with great industry. 

 The small diptera that haunt Pachylophus hover in the air about the flowers 

 until the stigmas push through the tip of the corolla, when they land and 

 move to the anthers as the flowers open, covering them in a black swarm. 



Constancy at the end of the season varied with the species and individuals, 

 but especially with the weather. On the first day after a protracted period of 

 rain or after snow, Bomhus juxtus visited flowers of all the genera still in 

 bloom, while on bright days the ^'■isits were usually confined to either Gera- 

 nium or Aster. A number of individuals were marked with colors and the 

 flight and visits followed for considerable periods. Bomhus bifarius went 

 to 627 florets on 52 heads of Aster during one flight, and then returned re- 



