62 EXPEUIMENTS MADE IN THE GARDEN OF THE SOCIETY 



XII. — Account of Experiments made in tJie Garden of the 

 Horticultural Socicli/^ in 1848, wilJi reference to the Potato 

 JJiseuse ; togetlier with some Observations on the same. By 

 Robert Thompson. 



From a comparison of symptoms connected with the disease as 

 exhibited by the crops of 1847, and those of the two previous 

 years, hopes were entertained, wlien drawing up a Report on the 

 subject twelve months ago, that ihe disease was on the decline. 

 In Vol. III. p. 63, it is remarked that, contrary to expectation, 

 some very fresh, healthy foliage was produced in the course of 

 July, 1847, by stems that had been prostrated by disease ; that 

 healthy tissue was in many instances protruded over the cankered 

 portions of the underground parts of the stems ; and that fresh 

 roots were subsequently emitted. In that season too there was 

 a sprinkling of fresh foliage remaining in many instances till the 

 natural period of decay in autumn. These symptoms, comjnired 

 with tlie premature!)^ total destruction of the haulm in the two 

 preceding years, 1845 and 1846, were considered favourable. In 

 those years the decay of tlie haulm was more rapid in some cases 

 tlian in others ; but in all cases the progress of the disease, 

 whether fast or slow, was still onward : there was no temporary 

 revival of the normal powers of vegetation exiiibited by the 

 stems and foliage after the blotches began to appear on them. 

 But the improvement, evidently commenced in 1847, continued 

 only for a short time in the present season, and then wds com- 

 pletely reversed, owing most probably to the excessively wet 

 period which ensued after the young tubers were formed. A 

 considerable quantity of rain fell in the months of March and 

 April, but May was unusually dry, scarcely 3-lOths of an 

 inch having fallen during the whole month. In fact, the potato 

 plants were then in want of moisture. Of this they had a suf- 

 ficiency in June and Julj\ Tiie quantity of rain in the.se 

 months was respectively 3*20 and 2*21 inches, the former being 

 T3 inch above the average, the latter somewhat below the 

 average. In the yet precarious condition of the potato, a quan- 

 tity of rain below the average would |)robably have been more 

 suitable ; but still what did fall seemed not to injure materially 

 the constitution of the plant, for intervals in which the atmo- 

 sphere posses.sed a considerable amount of dryness were frequent. 

 In August there were only five dry days throughout the month, 

 and 4"70 inches, nearly double the usual quantity of rain, fell. 

 Had the constitutions of the plants been perfectly sound, the 

 tubers would have been watery, excepting on open, dry .soils ; 

 but the tissue was not sound, and consequently incapable of 

 digesting such excess of moisture, and the putrescent form was 



