213 



observed with a hydrometer graduated to single 

 degrees. 



" This is not an absolutely accurate mode of observa- 

 tion, but the labour and time involved in making 

 estimations of specific gravities with the specific 

 gravity balance, renders this method impossible when 

 a large number of determinations have to be made, 

 especially as it is absolutely necessary to take a fail- 

 number of tubers from each variety to obtain an 

 average. As a matter of fact, it is frequently observed 

 that the differences in the specific gravity of tubers of 

 the same variety, and even from the same plant, vary 

 more than do those of different varieties. By taking 

 not less than twelve tubers of average size, it may be 

 assumed that at any rate approximately correct 

 results are obtained. The temperature of the solution 

 should, theoretically, be constant at 60 deg. throughout 

 the experiment ; but here, again, the variations are not 

 such as to appreciably affect the results obtained by 

 the immersion method. 



" Having obtained the at any rate approximate 

 specific gravities of the different varieties by this 

 means, it remains to interpret the results. 



" The first eight varieties of the thirty-one with 

 highest specific gravities TlOO and over, are all round 

 sorts, and the order, with one or two exceptions, is 

 from late to earlier sorts, the later being of the higher 

 specific gravity. The last eight sorts, 1*090 and under, 

 are all of the kidney type. The earliest variety of all 

 (Webber's Early Beauty), and that which gives the 



