PAPERS ON BIOLOGY AND AGRICULTURE 87 



portance. It is logical to suppose, however, that in case 

 the moisture content of a soil were low, the withdrawal 

 of even a small portion of this water by weeds might 

 prove very serious to the life of the corn and, in this 

 case, the rate at which weeds take water from the soil 

 and transpire it into the atmosphere would be a factor 

 of great practical importance. 



SUMMARY 



1. The relative rate of transpiration of Zea Mays, 

 as indicated by cobalt paper, is lower per unit area than 

 that of Polygonum pennsylvanicum, Sida spinosa, Am- 

 brosia artemisiifolia, Abutilon Theophrasti and Setaria 

 glauca. 



2. Of the weeds compared with Zea Mays, Ambrosia 

 artemisiifolia has the highest rate of water loss. 



3. The transpiration rates of Zea Mays and Setaria 

 glauca are more nearly similar than those of the corn and 

 any of the dicotyledonous weeds studied. 



BIBLIOGRAPHY. 



1. Bakke, A. L., Studies on the Transpiring Power of Plants as In- 



dicated by the Method of Standardized Hygrometric Paper. 

 Jour, of Ecology. 2:145-173, 1914. 



2. Bakke, A. L., Index of Foliar Transpiring Power as an Indicator 



of Permanent Wilting in Plants. Bot. Gaz. 60:314-319, 1915. 



3. Bakke, A. L. and Livingston, B. E., Further Studies on Foliar 



Transpiring Power in Plants. Physiol. Res. 2:51-71, 1916. 



4. Briggs, Lyman J. and Shantz, H. L., Transpiration During the 



Normal Growth Period and its Correlation with the Weather. 

 Jour. Agr. Research 7: 155-212, 1916. 



5. Briggs, Lyman J. and Shantz, H. L., Hourly Transpiration Rate 



on Clear Days as Determined by Cyclic Environmental Factors. 

 Jour. Agr. Research 5: 583-649, 1916. 



6. Cannon, W. A., A New Method of Measuring the Transpiration of 



Plants in Place. Torrey Botanical Club Bull., 32:515-529, 1905. 



7. Cox, H. R., Weeds: How to Control Them. U. S. Dept. of Agr. 



Farmer's Bull. No. 660. 1915. 



8. Cribbs, James E., Ecology of Tilia Americana: I — Comparative 



Studies of the Foliar Transpiring Power. Bot. Gaz. 68:262-286, 

 1910. 



9. Freeman, G. A., A Method for the Quantitative Determination of 



Transpiration in Plants. Bot. Gaz. 46:118-129, 1908. 



10. Kiesselbach, T. A., Transpiration as a Factor in Crop Production. 



Bull. (Research) No. 6. Nebraska Agr. Expt. Station, 1916. 



11. Livingston, B. E., Light Intensity and Transpiration. Bot. Gaz. 



52:417-438, 1911. 



12. Livingston, B. E., The Resistance offered by Leaves to Transplra- 



tional Water Loss. Plant World 16:1-38, 1916. 



