374 
Oti the Potato Disease. 
inevitable. By what means then, it may be said, are plants saved 
from total destruction after being nipped by frosts ? I answer, 
they frequently are entirely killed, but if bright sunshine ensues, 
as in the case I have cited, the tissue of the Irozen part is rup- 
tured, and the sap escapes as I saw it ; continuation of sunshine 
dries up the frozen parts, and the margin of the injured spot is 
healed by matter thrown out by the vital energy of the plant. 
If, however, a plant only slightly affected by frost is watered all 
over before the sun shines on it, and shaded for some time after- 
wards, it will recover entirely, as I have frequently experienced, 
if it be in good health at the time; but if it had been previously 
exposed to unfavourable conditions, by which its health had been, 
as it were, secretly undermined, I would not answer ibr its not 
becoming diseased or gangrenous in consequence : the vital energy 
of a plant depending upon certain conditions adapted to its own 
peculiar nature, and its diseases or premature death upon the 
partial or total deprivation of them. 
Slips * of diseased potato it is well known will produce disease, 
if inserted into others ; but simply bruising a sound potato will 
produce no such efTect. In order to ascertain the nature of canker 
still further, I inserted slips of apple-tree canker into some po- 
tatoes as well as into their stalks ; I also made a decoction of slips 
of cankered wood in a dormant state, and introduced it into the 
living stalks by puncturing them with the point of a knife ; I 
also inserted slips of diseased potato under the bark of apple and 
pear-trees, but by no one of these experiments did I succeed in 
transferring the disease, but a very little of the decoction soon pro- 
duced a blotch on the shoot of the vine (fig. 1, c). It appears, 
therefore, that the mortiferous principle of plants requires some 
affinity in the plant with which it is brought into contact, other- 
wise it will not assimilate its juices to its own condition, although 
not so close an affinity is required as for grafting or budding, as 
the canker of the apple-tree produced gangrene on the vine, with 
which a graft would certainly not unite. 
Amongst other eminent authorities, the opinion of Dr, Lindley 
has been throughout that the disease was produced by atmospheric 
causes. Lately, however, he has entertained a doubt whether 
Count Gasparin had not good reason for attributing it to some 
unaccountable miasma, such as causes cholera and other epi- 
demics, on account of the disease having appeared »nider circum- 
stances in which atmospheric changes such as I have before 
described did not occur. To this I can only say that Count 
Gasparin's tables of the weather may be accurate, but I cannot 
* They also destroyed carrots and onions, but did not injure cabbage- 
plants. 
