82 CARNEGIE INSTITUTION OF WASHINGTON. 



sugars, the term "total hydrolyzable carbohydrates," as defined above, 

 covering hydrolyzable carbohydrates of all types, soluble and insoluble. 

 On the other hand, it has been found that the insoluble polysaccharide 

 of this type do break down in the course of long confinement without 

 photosynthesis, but very slowly, and this fact, together with that of 

 the resistance of the echinocacti to desiccation, helps in a large measure 

 to explain the viability of these plants in spite of long starvation. 



Relation of the Rate of Root-growth in Seedlings of Prosopis velntina to the 

 Temperature of the Soil, by W. A. Cannon. 



In connection with general studies on the behavior of roots in soil, 

 the response of the roots of Prosopis seedlings to different soil tempera- 

 tures was investigated. The experiments were carried on with the 

 use of especially constructed thermostats, by which the soil in which 

 the roots were growing was usually kept within a variation of 0.5° C. 

 The shoots projected into the air, the temperature of which did not 

 usually vary more than 2° C . Observations for the purpose of detecting 

 changes in growth-rate that might occur were continued over periods as 

 long as 93 hours, during which time the rate of growth was observed 

 every 3 hours. The leading results may be summarized as follows: 



Growth was observed between 12° C. and 42° C. Growth in this 

 species may possibly occur at soil temperatures below 12° C, and 

 42° C. probably marks the maximum. The most rapid rate was 

 observed to occur at a soil-temperature about 34° C, at which point 

 a root with an initial length of 16 mm., grew 51 mm. in 12 hours. 



The rate of growth of roots in seedling Prosopis is not only a con- 

 dition of the temperature of the soil, but it also is closely correlated 

 with the length of the root. Generally speaking, roots less than 50 

 mm. in length exhibit, for a limited period, a progressive gi'owth-rate, 

 whereas roots much more than 50 mm. long, either maintain a fairly 

 constant rate or a declining one. 



Roof-growth of Prosopis velutina and Opuntia versicolor under Conditions of a 

 Small Oxygen-Supply in the Soil, by W. A. Canno?i. 



The work described below confirms and extends the conclusions and 

 results reported in Year Book No. 15, 1916. 



In the earlier work carbon dioxide alone and carbon dioxide with an 

 admixture of atmospheric air were used. In the studies here reported 

 carbon dioxide, commercial oxygen, and commercial nitrogen were 

 employed. The nitrogen-oxygen mixture which was used in many of 

 the experiments was determined by Professor H. M. Richards to be 

 2.67 per cent oxygen, and from this it was calculated that the nitrogen 

 contained about 0.71 per cent oxygen. 



The roots of seedling Prosopis exhibit a variable reaction to small 

 amounts of oxygen, depending, apparently, in the main on the length 



