Jan. 15, 192 1 



Tubers, Skins, and Sprouts of Potatoes 



633 



older than in the younger sprouts. Many changes in the percentage of 

 water-soluble to total phosphorus and in the distribution of the nitro- 

 genous substances follow the growth of the sprouts. The principal 

 period of growth of the sprouts under the conditions of this test occurred 

 during the period up to March, or from 60 to.150 days after the tubers had 

 been dug. From 1 50 days until the end of June, or 270 days after digging, 

 the increase in weight of the sprouts was less. The sprouts of the Irish 

 Cobbler tubers analyzed in June (sample 20) constituted 17 per cent, 

 while those of the Green Mountain tubers (samples 16 and 17) constituted 

 5.5 per cent of the total weight of tubers and sprouts. The Cobbler is an 

 early potato and the Green Mountain a late one. Both varieties had 

 reached their limit of sprouting in June under the conditions of these 

 tests. Apparently the growth-promoting principle is much more active 

 or is present in larger amounts in the Irish Cobbler than in the Green 

 Mountain and Rural New Yorkers. 



DISTRIBUTION OF NITROGEN, PHOSPHORIC ACID, AND ASH IN SPROUTS, SKINS, AND 



TUBERS 



The percentage distribution of nitrogen, phosphoric acid, and ash in 

 sprouts, skins, and tubers depends upon the relative weights of sprouts 

 and tubers. Although the sprouts of the Rural New Yorker tubers consti- 

 tuted 3.5 per cent of the total moist weight of tubers, skins, and sprouts, 

 they contained 6.32 per cent of the total nitrogen. The sprouts of the 

 Irish Cobbler on the same date constituted 13.33 P er cent of the total 

 moist weight and contained 14.81 per cent of the total nitrogen. Similar 

 ratios hold for the distribution of phosphoric acid and ash. This indi- 

 cates that the sprouts obtained the nitrogen, phosphoric acid, and ash in 

 certain proportions from the tubers, the tubers simply acting as reser- 

 voirs for the sprouts. The action of the sprouts was selective, as might 

 be expected in young, growing tissue. The solids of the sprouts con- 

 tained 4 per cent of nitrogen, while the solids of the tubers and skins con- 

 tained less than 2 per cent. In the Irish Cobbler the percentage of ash, 

 phosphoric acid, and nitrogen remaining in the tubers after sprouting 

 had ceased was less than 50 per cent of the total. 



Buckner (3) found 17.77 P er cen t of the total phosphoric acid in the 

 sprouts and 67. 1 3 per cent in the exhausted tubers. Because he found that 

 50 per cent or more of the mineral matter was left in the tubers, he thought 

 that a large amount of ash was necessary to bring about the katabolic 

 changes involved in sprouting. He obtained the following results : 



Material examined. 



New sprouts 



Skins 



Tubers 



Ash in 

 solids. 



Per cent. 

 9.91 



8. 14 

 4-37 



P2O5 in 

 ash. 



Per cent. 

 12. 56 



5-8 9 

 12. 4 



CaO in 

 ash. 



Per cent. 



0. 90 



1. 70 



•75 



MgO in 

 ash 



Per cent. 

 2. 72 



2.25 



K2O in 

 ash. 



Per cent. 

 40. 40 



40.33 

 53- 5 2 



Si02in 

 ash. 



Per cent. 



o-95 



8.45 



.60 



