On the Nature and Causes of the Decay in Potatoes. 541 
most numerous, and the progress of the disease in the tuber is 
along these vascular bundles, or along the course taken by the 
air. This is tlie very course which theory would indicate as that 
in which decay should progress, and I advance this as a powerful 
argument for the chemical nature of the disease. 
In Fig. III. a rough representation is made of a portion of a 
vascular bundle. This is surrounded by empty cells (bh), like the 
vessels themselves, filled with air. Hence the very structure of 
the vascular tissue of a potato is that which would most facilitate 
decay if the surrounding tissue were not powerful enough to 
resist these external influences. In the potato which has become 
diseased under ground, the disease, commencing at the junction of 
the underground stem, usually travels along the vascular tissue 
from one eye to the other, as shown in the diagram (Fig. IV.). 
Occasionally the disease commences by the vessels in the centre. 
Fig. IV. Diagram representing the section of a potato diseased. 
a, b, c. Eyes or buds. d. Diseased part. e. Vascular bundles. 
After the potato has been removed from the ground the dis- 
ease will commence at any bruised part where the putrefactive 
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