432 
On a Disease in Potatoes. 
man to whom I have before alluded, who says that the potatoes in 
his neighbourhood " have degenerated,* are degenerating, and 
ought to be regenerated."' I shall presently state reasons why I 
do not agree with him : but first let me give the history of some 
of his experiments. He first took some potato-sets from a field 
which M as much infested with Bobbin- Joans, and planted them 
in new ground ; in the crop wliich was produced, there were 
some, but not very many, of these abortions. He then planted 
sets of a fresh sort in the ground previously supposed to be in- 
fected, and the crop was entirely free from the deformity. 
At my suggestion a farmer in this neighbourhood has made the 
same experiments ; and though the result agreed with that ob- 
tained neaV Penzance only in this, that good sets produced perfect 
potatoes in ground which had previously produced Bobbin- Joans, 
I think it is enough to prove that the condition of the soil is not the 
true cause of the complaint. 
The point in which the issue of the experiments made here 
differed from that arrived at near Penzance, relates to the repro- 
duction of imperfect potatoes from diseased sets. Here none 
such appeared ; but there was a good and liealthy crop. More- 
over I have planted in garden-ground the very Bobbin-Joans 
themselves, in which, if anywhere, the disease must have pre- 
vailed, and in due time I dug up an abundant return of potatoes, 
every one of which was sound and of full size. From the fore- 
going experiments it appears to be clear that the condition of the 
ground is not the sufficient cause of the effect, and there is also a 
reasonable presumption that disease or constitutional debility in 
the j)lant arising from the decrepitude of age, computed from the 
original sowing, does not explain the loss of energy in the plant 
which was so easily revived by renewed planting. Then, I think 
we must look about for other causes to account for the stunted 
growth described ; and the mode of planting the sets suggests 
itself as the most natural. There is some analogy between the 
effects thus produced, and the habit which may frequently be 
observed in the growth of certain bulbous plants. The common 
autumnal colchicum, for instance, if planted too deep, will make 
a shoot which stops short of the surface, and then forms a bulb in 
the position most favourable for its growth in the ensuing year ; 
and I have even seen cases, when the plant has been accidentally 
]:)uried very deep, where three or four of these bulbs have been 
Ibrmed at nearly equal distances from each other ; thus, as it were, 
making its journey to the surface by stages. Therefore planting 
too deep, I have no doubt, may in some cases be the cause of the 
production of Bobbin -Joans. The root may not have strength to 
* Note by Dr. Liiidley — " When potatoes degenerate, they produce 
tubers of bad quality, but not Bobbin-Joans." 
