S. G. Paine 481 



shows losses from rot ranging from 10 per cent, to 75 per cent. In 

 Galicia also the percentage of diseased plants was very high during 

 1907 — 1910; von Hegyi(8) reported that 40 per cent, to 60 per cent. 

 of the crop was attacked in some experiments in which "seed" from 

 a badly infected area was used. Although the extent of loss of potatoes 

 by bacterial disease is at present low, probably not more than 5 per cent. 

 of the entire crop of Great Britain, it may at any time become much 

 more serious, and in fact there are indications that it is steadily on the 

 increase. The Board of Agriculture ( 21 ) recognises two bacterial diseases 

 of the potato namely Blackleg and Broivn Rot ; these have been identified 

 by the outward symptoms and the presence of bacteria in the tissues, 

 but the actual isolation and identification of the causal organisms has 

 not been attempted. It seems therefore desirable that a thorough 

 investigation of these diseases should be carried out and the present 

 paper embodies the results of a study of the former disease as it occurs 

 in Lancashire. 



SYMPTOMS OF THE DISEASE. 



The symptoms of the disease known as "Blackleg" have been 

 described very fully by Appel(i) and more recently by Pethy bridge 

 and Murphy (15) so that it is unnecessary to give more than a brief 

 description of the general characters of the disease. It usually makes 

 its appearance early in the summer during June or July, and especially 

 when a spell of hot weather follows a rainy period. On looking across 

 an infected patch of potatoes one sees here and there a plant dis- 

 tinguished from the rest by the wilted and yellow appearance of its 

 leaves; these later become dark brown or almost black and very much 

 shrivelled. On close inspection the stem shows at the ground level 

 a blackened area which gradually spreads upwards as the disease 

 progresses. Such stems when pulled gently leave the soil with scarcely 

 any resistance, there being as a rule an entire absence of development 

 of tubers. The pith at the base of such stems is completely rotted 

 away leaving a hollow space surrounded by a more or less healthy 

 cortex in which the vascular bundles stand out very prominently in 

 virtue of a strong brown pigment in the walls of the vessels. If the 

 attack has occurred late in the summer the disease will have spread 

 from the main stem through the underground stems to the developing 

 young tubers, and if these are cut longitudinally through the "heel" 

 they show the vascular ring marked out by the same brown pigment 

 which stains the vascular bundles of the stem. In many cases this 



