ROOT VARIATIONS INDUCED BY CARBON DIOXIDE 
S ADDITIONS TO SOIL’ 
HA NOVEsS i: Bo Trost ana: Li YouEs 
(WITH NINE FIGURES) 
Under discussions of tropisms in plants it has been customary 
to include statements relative to the tropic influences of gases on 
plant roots. Primary investigations on this subject were made 
by Motiscu,’ using seedlings of Pisum sativum and Zea Mays. 
Gases were caused to flow past the roots of the plants, and tropic 
curvatures were reported for all the gases employed. BENNETT? 
repeated these experiments and concluded that the results obtained 
were hydrotropic. BENNETT made further studies with Zea Mays, 
Raphanus sativus, Cucurbita Pepo, Pisum sativum, and Lupinus 
albus, both in artificial and in so-called natural media. Studies 
made with the seedling roots in air gave no indication of aéro- 
tropism. Studies made in earth, when the sprouted seedlings were 
placed between blotting papers in pots of moist earth and then 
subjected to streams of carbon dioxide gas for periods varying from 
24 to 60 hours, gave no definite curvatures. 
Cannon and Free,‘ after working with Prosopis veluntia, 
Opuntia versicolor, Fouquieria, Coleus Blumei, Heliotropium peru- 
vianum, Nerium oleander, and Salix (probably S. nigra), concluded 
that ‘it seems probable that soil aération must be added as a 
factor of no less importance than temperature and water,”’ for 
these plants were found to have different responses to carbon 
dioxide added to soil. The — quotation is self-explanatory. 
t Contribution f R h Cl id Bacteriology Laboratories of Depart- 
ment = Horticulture, 7 irene Agrivultaral Experiment Station, Lafayette, 
India 
cu, H., Uber die Ablenkung der Wurzeln von ihrer normalen Wach- 
Gucethane durch Gase (Aérotropismus). Sitzungsber. Akad. Wiss. Wien. 
3 BENNETT, Mary E., Are roots aérotropic? Bot. GAZ. 37: 241-259- 1904- 
4 Cannon, W. A., and Free, E. E., The ecological significance of soil aération. 
Science N.S. 45: 1917. 
Botanical Gazette, vol. 66] [364 
