154 Some Experiments on the Growth of Potatoes, 



five inches below the surface, without manure ; the soil having the 

 year before been manured for a crop of Mangel Wurzel. 



It was expected that this would prove as large a space as any of 

 the kinds would occupy, and that therefore the rate of increase of 

 each would be accurately determined, because their leaves would 

 be as fully exposed to light and air as could ever be practicable. 



At the same time, for the sake of comparison, a selection of 

 twenty-five of the best or most well known sorts was taken from 

 the Society's collection and treated in a similar way ; with this 

 exception only, that as the tubers we had reserved for planting were 

 in all cases small of their kind, two were used instead of one. These 

 two were also accurately weighed. 



In order to secure the greatest possible accuracy in the experi- 

 ment, I took the precaution to weigh the tubers myself in a pair of 

 excellent scales furnished with drachm weights. 



During the summer the plants were earthed up three times ; but 

 no other care was taken of them. 



The tubers were all taken up in October, and after having been 

 carefully washed and dried were again weighed ; but it was not 

 thought necessary to use other than common scales and weights, 

 nor indeed would it have been easy, from the bulk of the potatoes, 

 to have done so. 



The result of the observations are combined in the following 

 Table A, in which the weights planted and taken up, are reduced 

 to drachms for the sake of the more clearly pointing out the rate of 

 increase ; to this is added a computation of the produce of each 

 sort per acre, under the mode of treatment made use of. 



