32 ProceedinxfS of the Roijal Irish Academy. 



VIII. Practical Considerations. 



We have no exact data on which to base any estimate as to the losses 

 eaixsed by this disease in this countiy, but they cannot be inconsiderable. It 

 may be pointed out that these losses occm- both iu the gi'owing crop and in 

 the stored produce, and further, that of these the latter is iu all probability 

 the greater. As stated previously, the diseased plants are scattered here and 

 there thi-oughout the field or plot ; and the loss of a small percentage of plants 

 would not cause a partieidarly appreciable diminution in the total jield. Iu 

 the pits, however, each diseased tuber may serve as a centre from which the 

 rot may spread to the suri'ounding healthy ones ; and it is quite possible, there- 

 fore, for a whole pit to be rendered more or less completely useless. 



An institictive experiment was perfonned, which shows that there would 

 be no difficulty in perfectly sound tuber's becoming infected by contact with 

 diseased ones. A soimd tuber which had been placed in water for twelve 

 hours, allowed to dry for a further twelve hoiu's, and finally soaked for another 

 tweh-e in order to make it thoroughly damp, and to induce a certain amoimt 

 of proliferation of the tissues at the lentieels, was painted over with a pm-e 

 culture of the organism, placed in a covered dish, and kept at laboratory 

 temperature. The liquid cultiue di'ained to a certain extent down over the 

 surface of the tuber, and a thin layer came to Ue between the latter and the 

 bottom of the dish. At this point infection took place thi'ough a lenticel, and 

 the tuber rotted in characteristic fasliion. A control tuber which was painted 

 with sterile water remained sound. That the soaking in water did not afiect 

 the vitality of the tubers is clear fr'om the fact that they have since produced 

 normal sprouts. In a pit, especially if made at a time when the tubers were 

 not thoroughly diy, or if faidtily constructed, so that wet was not properly 

 excluded, the conditions woidd be very similar to those in the above experi- 

 ment ; and it is easy to see how, by means of infection through the lentieels, 

 very serious rotting could take place. In order to avoid this, it is necessary 

 first to exclude attacked tubers fi-om the pit ; and, secondly, to construct it as 

 far as possible when the tubers are thoroughly dry, and in such a maimer that 

 it can remain dry, and also cool; for, of course, the rot is much accelerated by 

 a rise of temperature. 



It would, therefore, seem a wise precaution to remove and destroy, as far 

 as practicable, aU plants attacked with this disease, as soon as possible, fi'om 

 fields or plots where it appeai-s, in order that the tubers produced by them — 

 which, though they may be few, are bound to be diseased to some extent — 

 may not find theii- way to the pit with healthy ones. Lea\'ing such affected 

 plants and tubers on the laud means that the soil wiU, at least at these spots- 



