On a Disease in Potatoes. 
433 
reach the surface, and so transfers its substance to a more favour- 
able position. But this is a very imperfect solution of the diffi- 
culty ; for in a field where the culture has been equal, and appa- 
rently there has been no variation in the depth of the plants in 
different parts, Bobbin-Joans have occurred in one place, and 
been entirely wanting in every other. This same remark is appli- 
cable to the idea which suggested itself to me, that insufficiency 
of nourishment and the absence of light might account for the 
imperfect growth of the set, as described in the third volume of 
the Horticultural Society's Transactions, p. 48. It is there stated 
that potatoes covered with sand and placed in a cellar will pro- 
duce small tubers, exactly resembling the Bobbin- Joans. The 
author thus explains the phenomenon : — " The potato, from the 
abundant nourishment which the tuber affords to the embryo 
plant, has an extraordinary disposition to vegetate ; and it seems 
to be possible to place it in such a situation that the vegetating 
power, being prevented from exerting itself upwards, so as to form 
stem and leaves, should be employed in throwing out roots only, 
with their appendages." 
But I do not see how this cause can exist in the open field, for 
what is to prevent the vegetating power from exerting itself up- 
wards ? and I believe we must look in another direction for the 
natural history of Bobbin-Joan. The following circumstances 
seem to point to that direction ; and I submit them to the growers 
of potatoes as leading to a conjecture to be verified or contra- 
dicted by their experience. 
From a heap of potatoes lately turned, some of which had shot 
out to a considerable length, two or three examples have been 
brought to me in which the shoot had been suddenly stopped by a 
small tuber. On cutting open the potato, I found that the centre 
])art had entirely decayed away, and not more than half an inch 
remained of the substance next the rind. This, however, ap- 
peared to be perfectly sound, but I suspect was not so in reality. 
Furthermore, on referring again to the farmer from whose field 
I first got the Bobbin- Joans, and who had suffered severely in his 
qrop in the season before last, I learnt that the potatoes from 
which he had taken the sets which produced the defective crop 
had been drawn in very wet weather, and stowed away without 
being properly dried. They had remained in that slate ; and I 
have no doubt that incipient decay, though unperceived when the 
potatoes yjere cut, had produced some change in the substance 
unfavourable to the growth of the set. Heating by fermentation, 
or from any other cause, and perhaps frost, may produce the same 
sort of disorganisation ; and I think it is not difficult to conceive 
that the starch of the potato being prematurely changed into gum 
or sugar, and dissipated before the young plant is in a condition 
