170 On the Prevention of Curl and Dry -Rot in Potatoes. 
very decided influence in modifying or increasing the potato 
failure ; which, at first sight, seems hardly reconcilable with the 
supposition that such failure is dependent on the degree of ma- 
turity of the seed potatoes when harvested. I at once admit 
that if seed potatoes are kept in too large a heap and allowed to 
ferment, or if kept so warm as to induce excessive growth during 
winter, or in any other way are so treated as to weaken their 
vitality, the sets will many of them fail, and others make weak 
and unhealthy shoots, very much resembling, and possibly iden- 
tical with, curl. It must be borne in mind, however, that though 
I consider overripening of the seed to be the ordinary cause of 
curl, I by no means assert that it is the only one. I am well 
aware that deficient management will^ especially if followed by 
long drought, produce failing crops, and whether such failure is 
due to curl or not I can offer no opinion ; but the great puzzle to 
potato-growers has been that, with the most careful management, 
failures continually occur, and these failures may, I think, be 
generally traced to ripe sets. That the influence of season is 
great I should be the last man to deny, as in two instances where 
my potato crops were affected with curl (distinctly traceable to 
having used ripe sets) they continued to get worse so long as the 
drought lasted, but on the occurrence of heavy rains they improved 
very much ; and this is quite in keeping with my theory, as when 
once the plant has a stem and leaves whereby to elaborate 
nourishment from the atmosphere, and roots which purvey from 
below, a large supply of moisture will give it such an abundant 
flow of sap that the vitiated juices of the decaying set will both 
be very much diluted and the plant will derive sufficient vigour 
from external sources to outgrow a slight ailment ; whereas in a 
droughty season, the plant is much more dependent on the set, 
and this at such a time furnishes the poison in a concentrated form. 
The next objection I shall notice is, that one of the best 
ways of getting rid of curl hitherto known is to grow the potatoes 
intended for seed on a piece of old meadow or other land that 
has been long uncropped. This is easy of explanation. Fresh 
land contains a supply of food which has been accumulating^ for 
years, and accordingly produces a more luxuriant growth and 
later maturity. Every one must have remarked that in a dry 
season plants of all kinds are less fully developed, but ripen earlier. 
This is doubtless owing to the less liberal supply of nourish- 
ment which they receive ; for even where the land is abundantly 
manured plants cannot avail themselves of it without moisture. 
When a plant has attained a certain stage of growth, even though 
considerably below its ordinary development, should its supply of 
food be stinted, either in consequence of drought, or of a scarcity 
of the necessary elements in the soil, it will at once proceed to 
