DEPARTMENT OF BOTANICAL RESEARCH. 71 



Influence of Soil Aeration upon Growth of Shoots, by W. A. Cannon. 



In connection with studies on the direct reaction of roots to aeration 

 conditions of the soil, which have been reported from time to time, 

 work has been begun on the influence of soil aeration as a factor in the 

 growth of shoots. This as an environmental factor of plants has not 

 been properly evaluated. It is impossible to tell by inspection, or field 

 studies, in what way and to what degree the aeration of the soil affects 

 growth of the shoot. Because, for example, plants may occupy 

 porous soils, it does not necessarily follow that the oxygen requirement 

 of the roots is high. That, as a matter of fact, adequate aeration is 

 necessary in some species to water absorption is known, ^ and it is also 

 known and reported^ that different species of land plants which may 

 live in the same community may nevertheless have unhke root-oxygen 

 relations. Such being the case, it is expected that survival may in 

 some instances be found to be largely bound up with the relation of 

 the roots to oxygen in the atmosphere of the soil. It must be con- 

 sidered especially important in this connection, particularly where 

 oxygen deprivation causes cessation of the growth of the root, to deter- 

 mine the relation of this fact to the possible continuation of the growth 

 of the shoot, as well as to determine the relation of the growth of the 

 shoot under such circumstances to environmental factors, aside from 

 and in addition to inadequate soil aeration. In fact, the general rela- 

 tion of the plant to soil aeration is of very great ecological importance 

 and merits investigation. 



In the preliminary experiments, a variety of garden forms have been 

 mainly used, and in addition a potato hybrid, Solanum fendleri X 

 S. tuberosum Fs^, and Eriogonum sp., a species native to the vicinity 

 of the Coastal Laboratory, were experimented with. The methods 

 used were the same as in the case of the root-soil-air studies above 

 referred to, with the addition of the employment of a MacDougal 

 auxograph to record shoot-growth. Nitrogen was used to replace the 

 soil-air. The experiments were conducted in the greenhouse at the 

 Coastal Laboratory and the shoots were exposed to the ordinary con- 

 ditions obtaining in the house. The following are some of the leading 

 results : 



In all of the plants of which the behavior of the root was observed, 

 root-growth ceased in an atmosphere of nitrogen, although in certain 

 species it continued 24 hours or over in such an oxygen-free soil atmos- 

 phere. 



Usually the replacement of the ordinary soil-air by nitrogen induces 

 a slowing of the growth-rate of the shoot. Upon the renewal of the 

 usual soil-air conditions, shoot-growth increases in rate, and may 

 become normal, provided the exposure to nitrogen has not been of 



1 Carnegie Inst. Wash. Year Book for 1916, p. 78. 



2 Ihid., p. 74; 1917, p. 82; 1918, p. 81. 



* Carnegie Inst. Wash. Year Book for 1918, p. 87. 



