214 



lowest yield, is of the lowest specific gravity ; and 

 the variety (Imperator) which gives the heaviest yield, 

 and is almost the latest, gives the highest specific 

 gravity. 



" The differences in the specific gravity of tubers, 

 assuming that there are no cavities in those taken for 

 the determinations, depend on the varying proportions 

 of water and of dry constituents respectively contained. 



" It is probable that these variations 'are this year 

 greater than usual, in consequence of the drought, 

 which has affected some varieties more than others, the 

 variations so caused being also, perhaps, connected with 

 the relative leaf surface from which evaporation takes 

 place. 



" The average percentage of water in potato tubers is 

 about 75, the extreme variations with different varieties 

 and different cultural conditions, being between 68 arid 

 82, or between 32 and 18 per cent, of dry, solid matter. 

 So far as the writers are aware, estimations of the 

 specific gravity of different varieties of potatoes, with 

 a view to determining their relative value for feeding 

 or other purposes, have not been made to any extent in 

 this country, probably because the tuber is not largely 

 used here for cattle-feeding purposes or for the manu- 

 facture of starch or spirit, to which latter purposes it is 

 largely put on the Continent, In view of the prob- 

 ability that heavier crops of field potatoes may be 

 grown in this country in the future, through the 

 introduction of disease-prevention remedies and later 

 and more prolific varieties, and that the tubers may 



