344 CARNEGIE INSTITUTION OF WASHINGTON. 



The Taxonomy of Haplopappus, by H. M. Hall. 



The work on this complex group of the Composite has consisted largely of 

 field studies on variation and the assembling of materials for garden experi- 

 ment and statistical investigation. A few species have been transferred to 

 new habitats in order to test the nature of their characters. Thus, H. 

 apargioides of the non-alkaline meadows has been transplanted to alkaline 

 soils of the desert borders, while H. racemosus of the latter habitat has been 

 carried to the alpine meadows, about 20 plants of each species being used in 

 the experiment. Intensive herbarium studies of the relationships of the 

 subgenera, species, and smaller variations are now under way, with the 

 object of presenting a detailed classification in the near future. 



Rubber Plants, by H. M. Hall and Frances Long. 



The work of the year on rubber plants has been restricted to the more 

 intensive study of the most promising genera, Chrysothamnus and Asclepias. 

 Samples aggregating several hundred pounds have been assembled and sub- 

 mitted to experts for tests as to the amount and quality of the rubber and 

 fiber present. A considerable number of plants of Chrysothamnus, represent- 

 ing 5 different forms, have been brought into special gardens in California and 

 Nevada for the study of variation, and some have been transplanted into fields 

 to permit cultivation and selection. 



Studies of Asclepias subulata at Sentinel, Arizona, show that its pollination 

 is chiefly effected by Anosia berenice. The community of this species, which 

 is the most extensive known at present, has been mapped to permit tracing 

 its changes in detail from year to year, and some of the plants have been 

 pruned annually to determine the effect upon the rubber-content of the 

 different shoots and to throw fight upon the possibility of harvesting the crop 

 by mowing. 



Latex and Laticiferous Tissue, by Frances Long. 



Material of 75 species of latex plants has been collected and preserved for 

 the study of variations in the development and occurrence of laticiferous 

 tissue. A method of differentiating the rubber-content of latex vessels has 

 been developed, in which the material is stained in toto and then sectioned. 

 Microchemical tests have been used to determine the latex in various parts of 

 the plant at different periods of growth, and special attention is given to the 

 origin of laticiferous tissue, its function, and relation to other tissues. 



In the hope of determining the factors that affect the latex-content, three 

 of the most important species of Asclepias, namely, subulata, sullivanti, and 

 galioides, have been grown in 5 different soils of known texture and water- 

 content, from sand to clay loam. Seedlings of the same age were planted in 

 pots of uniform size and placed under the same conditions. Soils were also 

 made up with varying amounts of alkali, and the seedlings planted in these in 

 sealed containers to permit determinations of the rate of transpiration and 

 growth and the relation of these to latex production and rubber-content. 



Absorption of Nutrients at Various Depths in Relation to Crop Yield, by 



J. W. Crist and J. E. Weaver. 



The original problem has been extended to include not only the amounts of 

 nitrates and phosphorus removed by crops at depths beyond the usual culti- 

 vation, but also the effect upon yield. Barley was grown under field conditions 



