7() The Potato. 



when the disease was most destructive, earthed the stalks up 

 very high, and saved his crop most effectually ;" again, on p. 75, 

 " few or none of the potatoes so grown were diseased." The 

 question then arises, icliat is tJie disease ? 



Very numerous and varied replies have been made to this 

 question, many of them unworthy of consideration. If examined 

 with the aid of a powerful le:is, the spot appears to be regularly 

 five-sided, angular, with one of the angles considerably pro- 

 truding beyond the others ; the centre is dark brown or black, 

 shading away to a lighter tint towards the confines, which are 

 marked frequently, but not always, by a line deeper in tint than 

 the colour wit'iin. The angle projecting is not confined or 

 limited to any one of the five angles. In the mulberry, the leaf 

 being thicker and broader, there frequently are many patches on 

 one leaf, and it can be easily seen that the protruding angle 

 points in diverse directions ; in the potato leaf it is rare to find 

 more than 3 patches of disease, but the diverse direction of the 

 angularity is equally perceptible ; outside the confines of the 

 patch may be seen numerous vessels filled witli a reddish brown 

 appearance, radiating into the sound substance of the leaf, and 

 every here and there apparently anastomose Avitli each other, 

 forming as it were a rayed plexus, around the central spot ; if the 

 evenings be moist and chilly the progress of the disease is 

 rapid, it soon reaches the stem, Avhen the leaf droops and soon 

 becomes puckered and shrivels up. If we now look at the 

 centre of the blackened spot, our unassisted eye cannot detect any 

 hole in the texture ; but if we hold it between our eye and a vivid 

 light, we shall perceive distinctly a hole. If we now turn the 

 leaf upside down, and examine it with a good glass, we shall find 

 that the edges of the hole are turgid and full, and presently we 

 shall see a fine line, or thread as it were, of silvery whiteness 

 arising from one side of the edge of the hole, and springing over, 

 like a bent bow, to the opposite ed^e, where it terminates in two 

 little knobs; and it will also be observed that this thread or 

 bright line has its whole edge knobbed or rugose, with similar 

 little knobs thickly arrayed on it. It was at once supposed that 

 these knobs or excrescences were the seeds or germs of the disease, 

 and on the discovery that sulphur in a confined place was a sure 

 and effective remedy, a great many plants grown in pots for the 

 purpose were exposed under favourable circumstances to the 

 action of the blackened portion surrounding the hole with 

 the supposed bloom on it. In a great nuinbcr of instances the 

 -contagion was speedy and certain, and from these plants so 

 infected other sound plants both of the vine and potato were 

 again infected. Neither could the disease again taken from 

 the greenhouse, after undergoing three inoculations, first on 



