RESPIRATION AND OXYGEN. 21 



tubers after treatment with warm water. Hoffman and Sokolowski 

 (1910) showed that varieties of potatoes differed among themselves 

 in the intensity of respiration and the evolution of carbon dioxid, 

 and that the effect of water and nitrogen-content was not always 

 the same as in grains, since potatoes with high water and protein 

 content may respire less actively than those with low water and 

 protein. 



Appleman (1914) found that potato tubers could be sprouted 

 at any time during the rest period by removing the skin and supply- 

 ing proper conditions for growth, including the maximum partial 

 oxygen-pressure of the atmosphere. Subdued light stimulates 

 growth in buds on new tubers with slightly suberized skins, probably 

 owing to the greater oxygenation of the tissues by photosynthesis, 

 as this disappears when the skin is removed. The rest-period in 

 new potatoes is shortened by treatment with hydrogen peroxide, 

 which is decomposed by catalase in the tissue, liberating free oxy- 

 gen. It is concluded that the elimination or abbreviation of the 

 period of rest is correlated with increased absorption of oxygen. 



In a study of the relation of catalase and oxidases to respiration 

 in the potato tuber (1916 : 223) Appleman determined the rate of 

 respiration and the activity of catalase and the oxidases under a 

 variety of conditions. He confirmed his earlier result that exposure 

 to ethyl bromide gas greatly increased respiration, and found a simi- 

 lar increase in the catalase activity, but none in that of the oxidases. 

 The effect of cold storage was to nearly treble the respiration, and to 

 increase catalase activity nearly 50 per cent, while slightly reducing 

 oxidase activity. Greening increased respiration and catalase activ- 

 ity a little and reduced slightly the oxidase action. The former were 

 also greater in the seed end than the stem end, while the latter was 

 practically the same. A difference of about 40 per cent in the respi- 

 ration of two varieties was closely reflected in the catalase, but not 

 in the oxidase activity. The author's conclusion is that there is no 

 correlation between oxidase activity and the rate of respiration, but 

 a very striking one between this and the catalase activity of the 

 potato juice. He also finds (1918 : 209) that the catalase activity 

 of the juice of sweet corn is a fair index of the respiration of the 

 tissues, and concludes that catalase activity is invariably correlated 

 with the oxidation processes of respiration. 



Crocker and Harrington (1918 : 171) have shown that there is a 

 similar correlation between catalase activity and respiration in the 

 seeds of Johnson grass, but not in those of Amarantus. As a rule, 

 the catalase activity of seeds seems to parallel physiological behavior 

 much more generally than does oxidase activity. 



Bartholomew (1913, 1915) applied the name blackheart to a dis- 

 ease of the potato tuber in which much of the tissue is dead and black. 

 He showed that it was due to tissue change caused by overheating 



