Disease in Plants. 189 



The growth of the potato-plants varied very much in the three 

 boxes. 



In Box I. (pure turf) and Box 111., which had received no 

 ammonia, the shoots were visible above ground on the 10th of 

 June. In Box II. they made their first appearance 10 days later. 



The growth of the tops in Box III. was much more rapid than 



in the two others. By the beginning of July the stems in this 



box were almost twice as strong and tall as those in the other 



boxes. But towards the end of the period of vegetation the tops 



in Box. II. (dressed with ammonia) looked fully as luxuriant as 



those of Box III. The colour of the leaves and stalks of the 



plants in III. Avas brighter and of a more yellow green than in 



the others. On the 3rd of July the plants were earthed up ; 



flowerbuds appeared on the 9th of August in Box II., and in 



Box III. four days later. Towards the end of September the 



stalks began to wither, and on the 3rd of October all were taken 



up. The tubers and tops, on being weighed, gave the following 



results : — 



Tubers. 



Box I. Box II. Box HI. 



Turfalonp Turf with Turf withuut 



Ammonia. Ammonia. 



Grammes 2520 .... 30G2 .... 7201 



Proportion 100 .... 121 .... 285 



Weight of set tubers being 7-G .. ., 9-7 .. .. 21'7 



Tops. 

 I. II. in.' 



Grammes 1837 .... 3535 .... 2870 



Proportion 100 .... 192 .... 15G 



At these rates the produce of tubers per acre would have been 

 about — 



In Cox I., 112 cwt.; II., 136 cwt.; III., 320 cwt. 



The constitution of the soil, therefore, in III. was so favourable 

 that it far surpassed that of the best arable land, since, according 

 to the usual data, the maximum yield of such lands seldom 

 exceeds 180 cwts. 



The growth, both of tops and tubers, calculated as dry sub- 

 stance, exhibited somewhat altered proportions. The quantity of 

 solid matter and of water in the tops and tubers was as follows : — 



