The Poiatoe Plague. 49 
where the entire vegetation may be destroyed by too wet or 
too dry a season. 
These attempts to trace a general effect to partial causes 
appear to me very like the deductions drawn from the pre- 
tended rules of phrenology. J examine astranger’s head, and 
find the bump of destructiveness, for example, fearfully prom- 
inent. I therefore pronounce lim a dangerous person; but, 
on inquiry, I learn that he is a man of remarkably benign 
and quiet temperament. “That,” says the phrenological the- 
orist, “is because his organs of benevolence and reverence 
are equally developed, and neutralize his destructiveness.” 
What practical use can be cut out of a science that defines no 
limits or proportions? 
In like manner, “one intelligent farmer (we quote from 
the report above mentioned,) on his own farm, where the soil 
was porous, lost none of a crop yielding two thousand bushels ; 
while of a field he purchased on a neighboring farm, where 
the soil was clayey, and retained much water, he lost the 
greater part of the crop.” Hence he argues that the soil and 
season together caused the injury, and so, undoubtedly they 
did; but, supposing there had been a diouth, the seed plant- 
ed in clay must have fared best. No general rule can be 
deduced from any such success or failure. From this and the 
concurrences of many other like instances, however, 1 draw 
the inference that a light soil is more congenial to the potatoe 
family, generally, than a heavy one. 
Another set of theorists attribute the potatoe disease to 
flies, or other insects. These, however, as far as satisfacto- 
rily observed, appear to be no other than have been always 
found upon the potatoe, without producing any injurious 
effects. They are the common aphis or vegetable louse, and 
flies which confine their ravages to the leaves. It might be 
argued in favor, or rather in disfavor of these parasites, that, 
by injuring the leaves, they deprive the tuber of its proper 
5 
