M. D. Glynne and V. G. Jackson 239 



cortical than in the medullary area. The percentage of nitrogen in the 

 fresh material does not vary greatly in the different zones while the dry 

 matter varies much. It follows that the percentage nitrogen in the dry 

 material varies considerably in the opposite direction to the dry matter. 



Again Condon and Bussard divided the tuber by two cuts at right 

 angles to the long axis, into an umbilical, an intermediate and a ter- 

 minal region. Each of these they divided into zones as before. They 

 found that the general relation of the cortical, the outer and inner 

 medullary zones to each other is the same in each of the three parts. 

 The cortical zone is always drier and poorer in nitrogen than the internal 

 medullary, and the external medullary is intermediate between the two. 



Shortly after the appearance of this work, Frisby and Bryant (4) 

 pubhshed analyses of different zones of the American variety ' White 

 Star.' Their method of zoning differed from that of Coudon and Bussard. 

 They scraped off both the dry brown outer covering which they termed 

 the "outer skin" and the layer immediately below this, the "inner 

 skin." The latter contains whatever colouring matter is present in the 

 tuber. The remaining flesh was treated as a whole. Their results are 

 shown in Table II. 



Table II. Composition of Different Zones of the Potato Tuber. 



Frisby and Bryant. 



% nitrogen % nitrogen 



°o of % dry in fresh in dry 



Variety Zone whole tuber matter material material 



WhiteStar Skin, outer 2-5 19-9 0-43 2-16 



„ inner 8-5 16-8 0-36 2-14 



Flesh 890 18-9 0-32 1-69 



Skin, outer and inner 110 17-5 0-38 214 



The inner and outer skin taken together constitute 11 per cent, of 

 the whole tuber, while the skin or "enveloppe" of two varieties analysed 

 by Coudon and Bussard form respectively 8-02 and 9-57 per cent, of 

 the whole. A certain variation with the size, shape and variety of the 

 tubers is inevitable. The figures quoted therefore approximate sufficiently 

 to support the supposition that the two skins referred to by Frisby and 

 Bryant correspond roughly to the whole "enveloppe" or skin of Coudon 

 and Bussard. Further Coudon and Bussard admit that part of the .sub- 

 cutaneous layer always adhered to the skin when it was removed. This is 

 very difficult to avoid, but Frisby and Bryant took particular precau- 

 tions against it. 



Unfortunately some confusion has arisen from Frisby and Bryant's 

 suggestion of the terms fibro- vascular or cortical layer for the inner skin. 



16—2 



