Dec, 1922] HAWKINS EFFECT OF LOW TEMPERATURES 
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rearrangement and partial splitting rather than by a breaking down of the 
molecule to CO2 and H2O, while at low temperatures in the presence of 
larger amounts of oxygen the molecule might be more completely decom- 
posed. Experiments at constant temperatures carried out for long periods 
will undoubtedly furnish some idea of the amount of CO2 given off at these 
temperatures under the conditions existing in the tissue. Some work of 
this type is in progress at the present time and wijl without doubt add much 
to our knowledge of the subject. Some good, simple method of measuring 
more directly the energy changes involved in respiration is urgently needed. 
Changes in the chemical composition of the product, while not always 
of value in indicating the constituents used in respiration, are of interest 
in themselves. The effect of low temperatures on changes which take place 
in carbohydrates in plants is of especial interest, and a number of investi- 
gations have added to our knowledge of this subject. Miiller-Thurgau^ 
found that in potatoes stored at low temperatures (o°-6° C.) sugars accumu- 
lated and starch was broken down more rapidly, while if the temperature 
was raised (to 8°-io°) the sugar disappeared and starch was formed again. 
He explains these phenomena by differences in the velocity at which the 
various reactions involved take place and differences in the optimum 
temperature, and there is every indication at the present time that this 
explanation is valid. Appleman,^ working with white potatoes, found that 
the carbohydrate changes are dependent on temperature and was able to 
corroborate much of Miiller-Thurgau's work. Hasselbring and Hawkins^ 
have shown that the carbohydrate changes in sweet potatoes are apparently 
similar to those in white potatoes. There is, of course, a higher sugar 
content in sweet potatoes, the cane sugar especially being much higher at 
the 'low temperatures. Sweet potatoes are usually stored commercially at 
relatively high temperatures (io°-i2° C), and at these temperatures if the 
roots have been properly cured they may be stored in good condition for 
a long time. If the temperature is lowered to 0° C, or even to 5° C, they 
become very susceptible to infection by micro-organisms and soon decay, 
especially if they are removed from the cold storage to a higher temperature. 
While it is not within the scope of this paper to discuss this phase of the 
subject, it is interesting to note the decrease in resistance of these roots at 
the low temperatures, which parallels the increase in sugar corttent. It is 
quite probable that these two reactions are not at all related but are merely 
concomitant. In the respiration experiments with sweet potatoes, it is 
^ Miiller-Thurgau, H. Uber Zuckeranhaiifung in Pflanzentheilen in Folge niederer 
Temperatur. Landw. Jahrb. 5: 751-828. 1882. 
^ Appleman, C. O. Biochemical and physiological study of the rest period in the 
tubers of Solanum tuberosum. Md. Agr. Exp, Sta. Bull. 183. Pp. 226. 1914. 
^ Hasselbring, H,, and Hawkins, L. A. Physiological changes in sweet potatoes during 
storage. Jour. Agr. Res. 5: 331-342. 1915. Respiration experiments with sweet potatoes. 
Jour. Agr. Res. 5: 509-517. 191 5. Carbohydrate transformations in sweet potatoes. 
Jour. Agr. Res. 5: 543-560. 191 5. 
