191 — 
first found at Oxford has disappeared; so that the only station 
now known is that about two and a half miles south of the vil- 
lage of Oxford. The plants grow in shaded alluvial soil, on the 
bank of the Chenango River. 
The Mode of Destruction of the Potato by Peronospora infestans.” 
The tuber of the potato being only an enormous development 
of the stem must possess all the parts that characterize the 
exogenous stem. That is, it should show the central pith, the 
woody or vascular layer, the bark and the epidermis. These 
may be readily seen with the naked eye on slicing the potato. 
The vascular layer appears as a semi-transparent line running 
along the cut surface about a quarter of an inch below the cuticle 
and rising to the eyes where it meets the layer that represents 
the bark. At these points the cuticle is exceedingly thin and 
here the assault of P. infestans is usually made. _ Its progress is 
marked by a black streak advancing from the eye along the layer 
of vascular tisstie which it destroys, either rising to the other 
eyes in its course or meeting similar hosts of enemies advancing 
from them. A layer of the bark immediately under the peel is 
attacked in the same manner about the same time. Two parallel 
black streaks are therefore visible advancing side by side below 
the skin of the potato. 
In these two layers the life of the potato resides and their 
destruction consequently ensures its death. To them the attack 
is confined. The starch -laden cells of the pith and those between 
the vascular layer and the epidermis are not injured. Indeed a 
tuber in this or even in later stages of decay, is one of the best 
sources from which can be obtained perfect starch-cells with their 
contents uninjured for microscopic study. 
Here the action of P. infestans ends. But other enemies 
soon troop in and complete the ruin it has begun. usisporium 
Solani abounds, but the greater part of what remains, the starch 
cells, is destroyed by Bacterium termo, the ubiquitous and ever- 
ready agent of destruction. This soon reduces the tuber to a 
mass of decay and to its action is principally due the smell arising 
from rotten potatoes. ’ E. W. CLAYPOLE, AKRON, Ohio. 
* Read before the Botanical Club of the A. A. A. S. at the Buffalo Meeting, 
August, 1886 
