210 ON THE PERONOSPOR^. 



Experience of the operations of the disease in past years has 

 generally shown that when one section of the Potato crop is 

 hardly hit, another as often escapes almost altogether. In average 

 seasons the disease has made its deadly effects most felt amongst 

 the mid-season kinds, whilst early and late ones have suffered less. 

 At other times the fungus has made an early appearance, and has 

 spared the later kinds, thus maintaining a sort of equilibrium, so 

 that an entire loss of crop has not often resulted. In noticing 

 this somewhat curious feature in the disease, we are brought face 

 to face with what is an undoubted problem in connection with its 

 operations, viz. — that the fungus seldom attacks any kind until it 

 has attained to a certain stage of maturity. Whilst matured kinds 

 may be almost destroyed by the fungus, the foliage of later sorts, 

 growing side by side with them, are untouched. There is, further, 

 the interesting fact that the worst phase of the disease attack is 

 generally condensed within a few weeks' space, from which it may 

 be assumed that the active germs of the fungus are operative only 

 during a certain period of time, the weather being probably the 

 guiding instrument as to the fixing of this particular period. A 

 few days of cold rain, with low temperature, or a period of 

 excessively hot sunny days, accompanied by heavy dews and white 

 mists at night, with occasional thunderstorms, may prove most 

 disastrous, broad breadths of luxuriant Potato foliage being 

 reduced in a few days to a blackened and putrid mass. 



In conclusion, I give the following practical suggestions which 

 were drawn up some time ago for a Hereford x\gricultural Society : — 

 I. — Burn the haulm, and all waste Potatoes, etc. Do not throw 

 them on the manure heap, because the mildew seeds will gain in 

 strength by resting in the manure, and this manure will help to 

 spread the Potato disease next season. 2. — Boil for a long time 

 all diseased Potatoes before feeding animals with them. It is 

 highly probable that the mildew seeds gain strength by passing 

 through the stomach of an animal, and the manure of animals 

 would thus become a powerful means of spreading the disease. 

 3. — Do not grow Potatoes on the same piece of land two years in 

 succession. Any mildew seeds (resting spores) which may rest in 

 the ground from last year's crop will begin to grow about the 

 middle of May, but will probably perish if they cannot find 



