DEPARTMENT OF BOTANICAL RESEARCH. 



87 



by nitrogen. The soil was the same in all cases and the plants used 

 were selected for similar age, size, and condition. Approximately 700 

 grams of soil were used in each case and the figures are in cubic centi- 

 meters of carbon dioxid produced per 24 hours, these figures being 

 reduced to the basis of 0° C. and 760 mm. pressure. 



The interesting feature of these results is the fact that when the plant 

 is present the production of carbon dioxid is greater in nitrogen than 

 in helium. The greater production of carbon dioxid from the cultures 

 containing tubers is obviously due to the much larger amount of 

 material suffering decay. While the quantitative precision of the 

 results given leaves much to be desired, and while the necessity of 

 numerous and careful repetitions is fully appreciated, it is believed 

 that the higher production of carbon dioxid in the nitrogen atmos- 

 pheres is a fact. It will be noted that this agrees with the visual 

 observation of more rapid root and tuber decay in nitrogen than in 

 helium, and also with the fact that the main root of the sweet pea did 

 not recover from nitrogen treatment but did from helium treatment. 



Interpretation of these results will not be attempted at present, but 

 it may be suggested that the results are consistent either with (1) a 

 stimulating effect of nitrogen on the bacterial actions which may be 

 assumed to be responsible (whether primarily or secondarily) for the 

 observed root decay, or with (2) a depressing effect of the helium on 

 this bacterial action. A stimulating effect of nitrogen is not unthink- 

 able in the light of the known existence of nitrogen-utihzing anaerobes. 

 A depressing effect of helium, if real, would presumably be due to some 

 impurity active against the anaerobes, but not against the aerobes. A 

 specific effect of hehum is extremely unUkely, and, as noted, the helium 

 has been tested for deleterious impurities, of course under aerobic 

 conditions. 



ECOLOGY. 



The Vegetation of a Desert Valley, by Forrest Shreve. 



The work on the vegetation and soils of the Avra Valley, which was 

 begun in 1918, has been continued. The mapping of the general types 

 of vegetation has been extended over a larger area, with a view to 

 ultimately extending it over the whole drainage basin. The character 



