1918] NOYES, TROST, & YODER—ROOT VARIATIONS 373 
Summary 
1. Plants respond differently to carbon dioxide gas added to the 
soil in which they are grown. 
2. The roots of the Christmas pepper, head lettuce, radish, and 
string bean were all found to be affected Bes additions of carbon 
dioxide gas to the soil. 
3. The effects of carbon dioxide on root development were 
greater than those on the aérial portions of the plants. 
4. The intermittent and constant applications of the carbon 
dioxide gas did not affect the roots of all the plants to the same 
extent. 
5. The effect of the gas was not the same for the different plants 
used, although a constant treatment of 650 cc. of carbon dioxide 
gas per hour was apparently preventative of normal root develop- 
ment. 
6. Decaying organic matter is held to be beneficial to growing 
plants. Cases have been cited by others where turning under 
immense amounts of green material has hurt the land temporarily; 
therefore the results obtained in these experiments lead to the belief 
that the carbon dioxide content of garden soils is sometimes 
detrimental to the root development of some plants growing in 
the garden. 
7. The conclusion of CANNON and FREE that soil aération must 
be a factor of no less importance in plant growth than water and 
_ temperature is supported. 
PURDUE UNIVERSITY 
LAFAYETTE, IND 
