DEPARTMENT OF BOTANICAL RESEARCH. 59 



similar excessive swelling of the ''ammonated" agar is obtained. 

 The "kaliated" agar swells about the same as pure agar in a solution 

 of KOH. Swellings in solutions of ammonium chloride and ammon- 

 ium acetate are not higher than those in water. 



The addition of a fresh solution of ammonium hydroxide affects 

 distinctl}^ the subsequent swelling of the already partially hydrated 

 agar. Thus, the increase of agar in water = 100; in 0.01 N NH40H = 

 25. If, after swelling to 25 ui O.OIN NH4OH, the hydroxide solution 

 is replaced by water, the agar will swell further to 73. ^^^len agar 

 plates are thus allowed to swell alternately every 12 hours in water 

 and O.OIN NH4OH, there is at fu-st swelling in both XH4OH and H2O. 

 As the hydration continues, the swellmg in NH4OH becomes slight and 

 finally there is a shrinkage in the NH4OH with a subsequent swelling 

 again in the water. However, the total swelling thus attained greatly 

 exceeds that in water or NH4OH alone. Similarly, alternations with 

 glycocoll and water also produce swellings in excess of those obtained 

 in either one alone. 



Effect of a Diminished Oxygen-Supply in the Soil on the Rate of the Growth 

 of Roots, by W. A. Cannon. 



Studies on the reaction of roots to a soil atmosphere poor in oxj'gen 

 or to one ha\dng an excess of carbon dioxid, which have been reported 

 in the Year Book,^ have been continued and extended so that they 

 include a number of different species for the most part not previously 

 used. Among the species studied are Erigeron nudum, Juncus sp., 

 Mesemhryanthemwn oequilaterale, Opuntia versicolor, PotentiUa anserina, 

 and Salix sp., and of cultivated plants the following: alfalfa, barlej^, 

 onion (market-garden), pea, and rice. A wide range in habit as well as 

 a great diversity in habitat is thus represented. Juncus, PotentiUa, 

 and Salix occur in very moist soils, if not saturated, throughout the 

 year. Erigeron is found in the pine forest at Carmel and hence in sandy 

 soil which is never saturated with water. Mesemhryanthemum grows, 

 escaped, at Carmel under conditions not greatly unlike those to which 

 Erigeron is subjected. 



In the experiments the plants were grown in glass tubes under con- 

 trolled conditions so far as possible. The experimental atmosphere 

 employed was composed of atmospheric ah-, to which commercial 

 nitrogen was added, or of cylinder nitrogen alone. The latter contains 

 about 0.5 per cent oxygen. In certain experiments commercial ni- 

 trogen was passed through alkaline pjTogallol to remove the small 

 amount of oxygen jDresent. The composition of the soil atmosphere, 

 the effects of which on root-growth were observed, is as follows: 2 per 



1 Cannon, W. A., Carnegie Inst. Wash. Year Book for 1916, pp. 74, 75; Year Book for 1917 

 pp. 82-83; Year Book for 1918, pp. Sl-8.3. 



Free, E. E., and B. E. Li\-ingston, Year Book for 1915, pp. 60-61. 

 Lmngston, B. E., and E. E. Free, Year Book for 1916, p. 78. 



