M. D. Glynne and V. G. Jackson 



243 



Composition of the Tuber. 



Dry Matter. 



The average percentage of dry matter in different zones, determined 

 individually on six small, six medium and six large tubers, is: 



Table VII. Dry Matter in different Zones of the Tuber. 



SmaU 

 54—84-5 gms. 



Medium Large Average of 



139-5-169-2 gms. 184-9-259-9 gms. 18 tubers 



Zone 



Skin 



Cortical, outer 

 „ inner 

 Medullary, outer 

 „ inner 



°' of 

 whole 



2-78 

 27-54 

 24-68 

 31-32 

 13-67 



%dry 

 matter 



14-29 

 24-86 

 29-25 

 25-76 

 20-19 

 26-93 



o' nf 

 whole 



1-85 

 20-29 

 20-11 

 36-43 

 21-32 

 40-40 



% dry 

 matter 



15-08 



23-43 



28-72 

 25-49 

 18-40 

 26-08 



%of 

 whole 



2-83 



18-11 



18-92 



39-95 



20-19 



39-03 



%dry 

 matter 



13-44 

 23-36 

 27-57 

 25-05 



17-48 

 25-52 



%dry 

 matter 



14-01 

 23-71 

 28-30 

 25-28 

 18-15 

 26-00] 



[Cortical, outer and inner 52-22 



Detailed results for each tuber are given in Appendix Table I. 



The percentage of dry matter in the whole cortical layer has been 

 calculated from the results obtained for inner and outer cortical layers, . 

 to facilitate comparison with results obtained by other investigators. 



The figures obtained corroborate the results of Coudon and Bussard 

 and other workers. The skin contains the lowest and the cortical layers, 

 taken together, the highest percentage of dry matter. The external 

 medullary zone has a higher percentage dry matter than the internal. 



Our figures also show that the inner cortical layer contains a higher 

 percentage of dry matter than the outer cortical. Thus the dry matter 

 increases from the outside of the tuber to the inner cortical layer and 

 then decreases towards the centre. In order to determine where this 

 decrease actually begins a sample of twenty tubers of varying sizes were 

 zoned as before, and in addition a zone adjacent to the inner cortical 

 layer was taken from the outer medullary zone. The corresponding 

 layers from all the tubers were analysed together. The results obtained 

 were: 



Table VIII. 



