l4 Scientific Proceedings, Royal Dublin Society. 



"spores," and settle it. When cut through, cliaracterislio internal markings 

 are also present, in the form of rusty-brown areas, confined in tlie earlier 

 stages to the tissues near tlie skin. It is in tliese discoloured areas that tlie 

 fungus mj'celium is then to be found. If such tubers be carefully watched 

 during the winter, it will be seen that the sprouts frequently begin to develop 

 much earlier than on healthy tubers, as is also tlie case with tubers 

 mechanically wounded, that the internal browning of the tissues gradually 

 becomes more and more extended inwards through the tissues, and tliat the 

 whole tuber becomes gradually destroyed. There is a race set up between 

 the destroying fungus on the one liand, and tlie still-living part of the tuber 

 on the otlier, and, in a very large percentage of eases, probably much more 

 than lialf of them, the fungus gains the victory, and tlie tuber becomes entirely 

 killed. On its surface, whitish pustules may often be seen, which, in some 

 instances at least, are due to fungi other than that causing the blight. It is 

 to be noted that there is little question of a resting period at all for the 

 potato, and much less for the fungus. Both are active, although naturally 

 the degree of activity depends to a certain extent on external conditions, 

 particularly temperature. If this be raised, the activity is increased ; 

 if it fall, it is diminished. If tlie tuber wins the race, tliat is if it 

 reaches planting-time, say in Marcli or April, with some still healthy 

 sprouts upon it, and a portion of its tissues still sound, this is largely because 

 the attack was in the first place a slight one, or the tuber was perhaps large, 

 and the distance from tlie attacked parts to the sprouts great, or possibly 

 because it was kept at a comparatively low temperature, so that the fungus 

 progressed but slowly. 



To have reached planting-time with one or two sound sprouts, and a 

 portion of the tuber still liealthy, is, however, only the end of the first lap in 

 the race. When such partially diseased tubers are planted in the soil, the 

 moisture and warmth present there cause it to be resumed with renewed 

 vigour. Experiments show that in a very large number of such cases no 

 plant at all comes above ground, the tubers and their sprouts, if any, becoming 

 completely killed before this is possible. In a few cases, however, the tubers 

 do succeed in sending small shoots above ground, but these, after a very short 

 time, succumb to the fungus which undoubtedly does grow up into them from 

 the diseased tubers. In the remaining cases, contrary perhaps to what would 

 be expected, the tubers, though originally diseased, give rise to what appear 

 to be perfectly healthy plants, that is plants free from Phytophthora, although 

 they may be somewhat less sturdj' than plants grown from healthy tubers. 

 Here, then, the potato plant has won the race against the fungus ; for the 

 sprouts develop and grow into healthy stalks, independent of the parent set 



