On the Cultivated Potato. 
28& 
{S. tuberosum), " It grows in its wild state on low hills ; extensive 
cultivation was successful until the year 1867 : the plant grew 
with an exuberance worthy of admiration, and disease in the 
nature of an epidemic was unknown. A local and transient 
disease had been observed, called ^ Ceniza y tahaco^ (A.shes and 
tobacco), caused by a fungus rendering the leaves white as though 
dusted with ashes : another mould caused a snuff-dusted appear- 
ance : these diminished, but did not hinder production. Then 
in 1867 an epidemic appeared suddenly ; it attacked the leaves 
only, leaving the tubers intact, and in all stages fit for food : the 
disease often runs its course in a single night. It is not para- 
sitic ; it is not impoverishment of the soil: the cause," says 
the writer, "resides in the atmosphere. In July 1867, a year of 
the greatest promise, in the last days of the said month there 
appeared in one night at daybreak two fields of earthed-up 
potatoes with their leaves completely withered : seen from a 
distance, there was a sombre black where previously there had 
been a cheerful green. We could not believe our eyes until we 
touched the reality. The failure was general, but not simul- 
taneous ; in all the valley of Lima the blight was most irregular, 
hit-and-miss, here a patch and there a patch. Later the virulence 
rather spent itself, and instead of one night the disease occupied 
in its work two or three days. The effect on the plants has 
been in proportion to the intensity and duration of the blight." 
The disease ran on unchanged until 1873, when "it was so bad 
it killed all the new varieties which had been obtained from 
California, Chincha, and Chili, l eafless plants were known to 
bud again, but only to die. Late-sown (August) potatoes gave 
a scanty yield : in the year 1877 even the potatoes planted near 
the sea were lost ; these hitherto had the greatest power of 
resistance. Potatoes are blighted at every age, but suffer most 
when they have been earthed-up. Cloudy and rainy days are- 
favourable, but above all things the blight appears to require 
moisture condensed on the leaves of the plants. During the second 
year, there was very dry weather until August, then drizzle, and 
the day of the blight, Saturday the 9th, towards night much 
rain. After this year the lucerne-buds suffered excessively from 
the same disease : simultaneously, in distant places, tomatoes 
also were attacked. Sometimes the disease begins with isolated 
patches of various size on the margins of leaves of the colour of 
tobacco, with a whitish border, then the ultimate fate of that 
field is sealed." The writer combats the mould theory, on the 
ground that all vegetable tissues in decomposition are thus 
attacked. " All experiments, and experiments have been nu- 
merous, have failed : sulphur-smoke once succeeded, but it is 
not cl^ar how it acted : artificial irrigation greatly aggravates ; 
VOL. XX.— S. S. U 
