33 



each year. Each year determinations of the specific 

 gravity of the " good " tubers, and of the percentages 

 in them, of dry matter, ash, and nitrogen, have been 

 made, and the results are annually given in the 

 " Memoranda." In the " small " potatoes also, the 

 specific gravity, and the dry matter, have always been 

 determined; in some years the ash, and in one year 

 the nitrogen was also determined ; but nitrogen might 

 suitably be determined in " mixed-year " samples only. 

 In the diseased potatoes the dry matter is determined 

 and sometimes the ash. 



The dry matter, the sugar, the nitrogen, and the 

 ash have, in selected cases, been determined in the 

 expressed juice of the tubers. In some cases the 

 amount of the nitrogen existing as albuminoids has 

 been determined ; and in some complete analyses of 

 the ash, both of the whole tubers and of the juice, 

 have been made. In a considerable number of cases, 

 somewhat similar methods of examination to those 

 adopted in the case of the sound tubers, have been 

 applied to the still white or incipiently diseased, and 

 to the separated discoloured portions, of diseased 

 potatoes. These various results are briefly referred to 

 in the heading to the Tables of composition of the 

 potatoes, in the " Memoranda;" and are of considerable 

 importance. 



The results of the experiments on Potatoes, both 

 those obtained in the field and in the laboratory, have 

 been pretty fully discussed in my Oxford Lectures ; 

 and a resume has been given in No. 78, 1888. 



It seems desirable that the sampling of the " good " 

 potatoes, and the determination of their specific gravity, 

 and of their percentages of dry matter, ash, and 

 nitrogen, should be continued so long as the field 

 experiments are maintained. But possibly the sampling 

 of the " small " and " diseased " potatoes, might be 

 discontinued after that of the crop of 1890, which is 

 the fifteenth of the experiments ; unless it should be 

 found desirable to follow up any special point in any 

 subsequent year, 



