IRISH GARDENING 



67 



If the tuber be of a red variety, the colour is 

 destroyed in this area. The diseased portion is 

 much less firm to the touch than the healthy, 

 and when squeezed a liquid is exuded. This 

 g-reater wateriness makes the clay stick to 

 affected tubers, even in dry soil. In advanced 

 stag-es the whole substance ma}- be reduced to 

 a pulpy mass. If a diseasetl tuber be cut, the 

 rotted part is usualK , but not aKvavs, oi' a dirtv 



experiments are still in progress which, it is 

 hoped, will clear up the practical problems 

 which the subjects present, it is, nevertheless, 

 possible to lay down some rules of the greatest 

 importance to practical men. And it should be 

 borne in mind that if these cannot always be 

 adhered to in the field, they can always be 

 followed in the garden and in small plots, w^here 

 the greatest danger of infection exists on 



A Large Potato Plant with several Stalks atiacked with Bi,\ck-stalk Rot, with a 

 BACKCiROiNn OE Healthv Plants. X'arietv "British Oiken." 



I'hotographed in July, 

 n'he photographs illustrating this paper are reproduced through the courtesy of the Royal Irisli Academy."' 



grey colour, which quickly takes on a pinkish 

 tinge, and finally becomes deep brown or almost 

 black. Badly affected tubers are quite useless 

 for any purpose. 



The cause oi' all these changes in the sub- 

 stance of the potato plant and its tubers is one 

 of those excessively minute organisms called 

 bacteria. The organism with which wc ;ue 

 immediately concerned is so small that it would 

 take about 15,000 of them placed end to end to 

 stretch an inch. 



With such a disease it is evident the aim 

 must be prevention rather than cure. Though 



account of the difficulty in the way of proper 

 rotation of crops. 



The first and most important rule is, that 

 diseased plants and all their tubers should be 

 dug up and destroyed as soon as ever the 

 disease appears. There are two very good 

 reasons for doing this. In the, first place the 

 rot is not confined to the growing season, but 

 may and does continue in the pits, particularly 

 if the latter are hot and damp. It has been 

 proved that these bacteria can penetrate the 

 skin of a healthy potato when kept in a damp 

 place, so that contact with rotting potatoes 



