394 



GROWTH OF PLANTS 



Critical storage temperatures for sugaring and sprouting. We have already 

 seen (Table 39) that the formation of reducing sugar falls greatly as 

 the storage temperature rises from 5° to 7° C (41° to 45° F), and still 

 further as the temperature rises to 8.2° C (47° F). All but a few varieties 

 can be stored at 8.2° C (47° F) for 78 days without accumulating enough 

 reducing sugar to interfere with chip making. A number of varieties can be 

 stored at 7° C (45° F) for 68 days without an interfering amount of reducing 

 sugar accumulating. It is probable that at 9° C (48° F) few varieties wUl 

 form reducing sugars in amounts sufficient to interfere with chip making, 

 even after months of storage. Even at 7° C (45° F) so little reducing sugar 

 accumulates that in any good de-sugaring variety a few days at 27° C 

 (81° F) will de-sugar them to a sufficient degree. 



Figure 155. Sprouts removed from 16 tubers of each of five varieties after storage 

 from Oct. 25, 1941, to Mar. 3, 1942, at T and 8° C (45° and 46° F); top row, 8°, bottom 

 row, 7°; varieties, left to right are: Irish Cobbler, Carman No. 3, Green Mountain, Houma, 

 Katahdin; the zero label {lower right) indicates no detachable sprouts were present. 



Sprouting is long delayed and the rate of growth of the sprouts is very 

 slow when tubers are stored at 7° C (45° F) . The sprout growth is con- 

 siderably faster at 8° C (46° F). Fig. 155 shows the difference in the degree 

 of sprout growth of five different varieties stored at these two temperatures 

 for about four and one-third months or from October 25 to March 3. 

 These tubers were harvested about the middle of August and were held at 

 room temperature until October 25; consequently the period from harvest 

 until the amount of sprout growth showTi had occurred was nearly seven 

 months. Even on June 3, nearly ten months from harvest, the sprout 

 growth for Irish Cobbler and Katahdin at 7° C (45° F) was very slight, 

 although it was considerable for the other three varieties. On June 3 the 

 sprout weight of the five varieties stored at 8° C (46° F) was two and 

 one-half times that of those stored at 7° C (45° F). While it is evident 

 that 7° C (45° F) is effective in delaying sprouting, it does lead to the 

 accumulation of a slightly excessive amount of reducing sugar. This 

 amount, however, is eliminated by a few days' storage at 27° C (81° F). 



