422 



GROWTH OF PLANTS 



Figure 170. Conditions of plants at four different stages at which mother-tubers 

 were amputated: A, stage 1; B, stage 2; C, stage 3; D, stage 4. 



analyses. The data in this table are given on the basis of the percentage 

 of the original total amount of each constituent remaining in the seed- 

 piece at each stage of development. Large and rapid losses in dry weight, 

 starch, and nitrogenous substances are shown. The losses are greater and 

 earlier in Bliss Triumph than in Irish Cobbler, also greater in 14-gram seed- 

 pieces than in 56-gram seed-pieces. Since starch constitutes a large per 

 cent of the original dry weight, a large loss of starch — 89 per cent in 

 Cobbler and 97 per cent in Triumph — means a large loss in dry weight, 

 75 and 90 per cent respectively. Moisture and soluble sugars increase in 

 Cobbler mother-tubers throughout the growth period; but with Triumph, 

 increase in the early season is followed by a later decrease. 



What does the mother-tuber furnish the growing plant that is necessary 

 for maximum yield? As is seen from the chemical data in Table 48, the 

 mother-tuber ceases to be of importance about the time the main nutrients, 

 especially starch, are exhausted. In Irish Cobbler mother-tuber, the 

 starch is exhausted later than in Bliss Triumph; also in the former the 

 mother-tuber has a beneficial effect on the growth of the plant for a longer 

 period. This at least indicates that the mother-tuber may be o'f importance 

 as a source of nutrients. Appleman ^ thinks growth-promoting substances 



