﻿. 1 PPLF.M. 1 \~REST PERIOD 



Under normal planting conditions potato tubers will not sprout 

 for several weeks after harvest. During this rest period certain 

 changes must occur in the chemical or physical situation of the buds 

 or their immediate environment which are essential to the release 

 of the growth processes. These changes are spoken of as "after- 

 ripening," using the term in its broadest sense. 



The carbohydrate transformations during the rest period are 

 dependent entirely upon changing temperature. 



Active diastase and invertase are present at all stages of the rest 

 period, but show no increase under normal growing conditions until 

 the tubers begin to sprout. 



The juice from tubers at the end of the rest period causes a 

 greater acceleration of the oxidation of pyrogallol than the juice 

 from new immature tubers of the same variety. The seed and stem 

 halves show no difference in the ability to oxidize pyrogallol even 

 after sprouting from the seed end. 



After-ripening does not involve protein hydrolysis. There is no 

 change during the rest period in the relative magnitudes of the fol- 

 lowing forms of nitrogen : proteose and peptone; diamino acids and 

 other bases; monoamino acids and amides. 



Protein, lipoid, organic extractive, and inorganic phosphorus cal- 

 culated to percentage of total phosphorus, each remains constant up 

 to the time of sprouting. 



The magnitudes of the substance studied are not all identical 

 in the seed and stem halves. The relative composition, however, 

 remains practically constant during the rest period in spite of the 

 fact that sprouting begins much earlier on the seed end. 



Metabolic changes involving the above forms of nitrogen and 

 phosphorus begin rather suddenly and are concurrent with sprout- 

 ing. The same is true of diastase. 



Drying causes rapid suberization of new skin and exposed sur- 

 faces. 



Suberization greatly reduces the permeability of the skin to 

 water and gases. 



Potatoes may be sprouted at any time during the rest period by 

 simply removing the skins and supplying the tubers with favorable 



