238 Dni Matter and Nitrogen in the Potato Tuber 



his results that the parts of highest specific gravity are all in one zone 

 which is nearer the periphery than the central part of the tuber, and 

 further from the end of attachment than from the sprout end. The 

 criticism of the coring method again applies to this work. 



Coudon and Bussard(3), two French investigators, gave in 1897 the 

 percentage dry matter and nitrogen in different zones of the tuber. In 

 zoning they followed the main physical divisions which can be seen with 

 the naked eye. The skin forms a corky covering surrounding the cortical 

 layer. The latter is generally the densest part of the tuber, and its inner 

 boundary is roughly marked by an incomplete ring of vascular bundles 

 whose branches ramify in the cortical and in the central zone. The central 

 or medullary area varies considerably in uniformity. The interior part 

 is very wet and translucent, and has branches known as pith rays which 

 penetrate the denser outer medullary region and sometimes reach the 

 surface of the tuber in the neighbourhood of the eyes. 



The zones taken by Coudon and Bussard are as follows: 



Skin. 



Cortical Zone. 



External Medullary Zone. 



Internal ,, ,, 



They express their results for nitrogen as percentage protein in fresh 

 material, i.e. total nitrogen x 6-25. For purposes of comparison we have 

 calculated the percentage of nitrogen in both fresh and dry material. 

 The results are shown in Table I. 



Table I. Composition of the Different Zones of the Potato. 



Coudon and Bussard. 



% nitrogen % nitrogen 

 % of % dry in fresh in dry 



A'^ariety Zone whole tuber matter material matter 



Bleuegearite Skin 9-57 1716 0-364 2120 



Cortical 34-66 27-53 0-306 1-110 



Kxtemal medullary 37-15 25-67 0-299 M66 



Internal „ 18-62 18-28 0-342 1-868 



Czarine Skin 802 17-79 0-360 2-022 



Cortical 37-72 2708 0-295 1089 



External medullary .3811 21-13 0-347 1-640 



Internal „ 16-15 15-52 0-348 2-241 



The percentage of dry matter is less in the skin than in the cortical 

 layer and decreases from the cortical to the internal medullary layer. 

 The percentage of nitrogen is greatest in the skin and is lower in the 



