495 



cailiiiess or lateness of the variety (diiratioii of the eliaracteristie period 

 of growth). Thus the total perceiit.aj;e h>ss from October to INIay 1 

 varied with tlie 3 early varieties from 4.87 to 8.4S; with the "> medium- 

 early varieties from 4.55 to 0.78, and with the 4 later varieties from 5.71 

 to 7.28 per cent. Siuee, according to Xobbe, about three fourths of the 

 loss may be attributed to loss of water aud only about oue fourth to the 

 respiration, the above losses wouhl indicate a loss of only l.li to li.l jier 

 cent of organic matter. These losses by keeping are believed to be 

 lower thau are usually assnnu'd and lower than those observed by 

 ISTobbe. 



The author refers to the two important factors in determining the 

 loss, i. e. dryness and temperature, the last of which was studied by 

 Miiller-Thurgau,* and he gives a brief rdsum6 of Midler's ol)serva- 

 tions. According to JMiiller three distinct processes go on in potato 

 tubers, namely, respiration, sugar formation, and retrograde starch 

 fornuition. It is explained that the respiratory process takes place in 

 the living protoplasm of the cells and consists of an oxidation of cer- 

 tain organic substances (sugar, etc.) through the atmospheric oxygen, 

 *the products of the process being carbonic acid and water. The inten- 

 sity of the process depends upon certain conditions, as age of the tubers, 

 temperature, quantity of material present which is cai)able of su])i)orting 

 the process, etc. Milller found tliat the process was more energetic the 

 more sugar the protoplasm had at its disposal and the higher the 

 temperature. 



The importance of the second process — the sugar formation — is readily 

 seen from the dependence of the respiratory process upon it. The sugars 

 formed in the tubers are cane sugar and glucose, the larger amount 

 being of the latter. This formation of sugar is believed to be from the 

 starch by means of a ferment, but this ferment can not be diastase, 

 since, according to the author, it does not occur in the tubers, and more- 

 over from starch diastase forms dextrin and maltose. Temperature 

 has a greater influence on the respiratory process than on the formation 

 of sugar, so that at lower temperature more sugar is produced than is 

 oxidized, and so accumulates. This fact explains the sweet taste of 

 frozen i)otatoes, for while scarcely any. respiration takes place at - 1° to 

 — 2° C, the sugar formation is only slightly abated at this low tempera- 

 ture. But the sugar formation is not accelerated by increased temper- 

 ature in the same proportion as the respiration is, so that it follows 

 that the amount of sugar iu potatoes depends upon the temperature at 

 which they have been kept. 



The retrograde starch formation, or the re-formation of starch from 

 sugar, takes place when potatoes which have become sweetare subjected 

 to a warm temperature for a time. According to Miiller's experiments 



*Bot, Ce-fttralbl., 19 (1882), No, 2; Lanilw, Jahrb., 1882, pp. 751-828, aud 1885, pp. 

 8.31-912, 



