M. D. Glynne and V. G. Jackson 241 



The results of Waterstradt and Willner and of East corroborate 

 those of Coudon and Bussard. The percentage of dry matter decreases 

 from the cortical to the outer and inner medullary layers. Nitrogen 

 does not vary greatly in the fresh material but on the whole the medullary 

 zone is richer than the cortical. This zone therefore contains a con- 

 siderably higher percentage of nitrogen in its dry matter than does the 

 cortical. 



The possible variation in composition between big and httle tubers 

 of the same variety must be considered in selecting a sample. Kreusler 

 and Werner (7) maintain that the proportion of dry matter varies little 

 in one variety, and in so far as it does it increases with the size of the 

 tuber. Drechsler and Wollny(8) showed by a great number of experi- 

 ments that in the same way the proportion of starch varies very little 

 with the size of the tubers. Dry matter determinations by Coudon and 

 Bussard on three sets each consisting of ten whole tubers are as 

 follows : 



Table V. Percentage dry matter in big, medium and small tubers. 



Weight 



There is very little variation in the proportion of dry matter in tubers 

 of different size. Coudon and Bussard therefore conclude that in taking 

 a sample, the size of the tubers does not appreciably influence the mean 

 composition of the sample. However they consider it advisable always 

 to use a number of whole tubers in carrying out analyses. 



PRESENT INVESTIGATION. 



The present investigation was carried out at Rothamsted on the 

 variety ' King Edward " grown on the Little Knot Wood field. The soil is 

 clay with flints lying on chalk. It is heavy for potatoes, but the crops 

 are in no way abnormal. During the season under consideration, 1917, 

 the average yield of three varieties was 5 tons per acre, while the average 

 for potatoes in England and Wales was 6-6 tons per acre. 



The potatoes were sown during the first week in May and were 

 lifted about the end of September. They were then put in a clamp. 

 The investigation was begun early in 1918. The tubers were taken 

 either directly from the clamp or from a dark cool room to which they 

 were later removed. 



