MEASURES OF INSECT COLD HARDINESS. 457 



SUMMARY. 



1. Cold hardiness to the intensity factor of low temperature 

 can be measured by moisture content, undercooling point, and 

 blood conductivity. 



2. Up to the time when a given insect can survive freezing, 

 undercooling is a reliable measure of cold hardiness. Beyond 

 the point when an insect can survive freezing, undercooling 

 measures but a part of the total cold resistance of a given insect. 



3. Conductivity measurements are found proportional to cold 

 hardiness throughout the whole year. In some insects there is 

 insufficient free body fluid in winter on which to determine 

 blood conductivity. 



4. For each species there is a different set of physical constants 

 which measure the cold hardiness of that species. 



LITERATURE. 



1. Bachmetjew, P. 



'01 Experimentelle entomologische Studien vom physikalisch-chemischen Stand- 

 punkt aus. Bd. I. Leipzig. 



2. Duval, M., et Portier, P. 



'22 Limite de resistance au froid des chenilles de Cossus COSSHS. Compt. 

 Rend. Soc. Biol., 86: 2-4. 



3. Harvey, R. B. 



'18 Hardening Process in Plants and Developments from Fiost Injury. Journ. 

 Agr. Res., 15: 83-112. 



4. Johnson, Earl S. 



'23 Moisture Relations of Peach Buds during Winter and Spring. Md. Agr' 

 Exp. Sta. Bull., 255. 



5. Muller-Thurgau, H. 



"86 tjber das Gefrieren und Erfrieren der Pflanzen. II. Theil. Lanclw. 

 Jahrb., 15: 453-618- 



6. Newton, Robert. 



'24 Colloidal Properties of Winter Wheat Plants in Relation to Frost Resistance. 

 Jour. Agr. Sci., 14: 478-191. 



7. Newton, R., and Gortner, R. A. 



'22 A Method for Estimating the Hydrophyllic Colloid Content of Expressed 

 Plant Tissue Fluids. Bot. Gaz., 74: 442-446. 



8. Payne, Nellie M. 



'26 Freezing and Survival of Insects at Low Temperatures. Quart. Rev. 

 Biology, i: 279-281. 



9. Payne, Nellie M. 



(In press.) Two Factors of Heat Energy Involved in Insect Cold Hardiness. 



Ecology. 

 10. Steinbauer, George. 



'26 Differences in Resistance to Low Temperatures Shown by Clover Varieties 



Plant Physiology, i: 281-289. 



