On the Potato Disease. 
371 
witherinfj circle was completed round the stem. Sometimes even 
then it will not give in ; the upper leaves will still retain their ver- 
dure in spite of it, while a particle ot" vital wood remains. (The 
Jersey Blue potato v. ill, in good laud, also stand out as stubbornly.) 
On the other hand, J have seen, not only in former years but in 
the present one, geraniums which had been carefidly nursed during 
the winter, destroyed in a few days by the same disease, caused by 
too sudden exposure to the variable weather of spring ; sometimes 
without, but more frequently with, a copious supply of pump- 
water. 
Analogous cases are mentioned by the celebrated Dr. Darwin, 
in ' Phytologia,' which I hope I may be allowed to introduce here, 
a3 they appear to accord so nearly with the phenomena of last 
season. He says, — " In the hot days of June, 1798, I twice ob- 
served several rows of garden-beans become quite sickly, and 
many of them to die, from being flooded for an hour or two with 
water from a canal in the neighbourhood ; which I ascribed more 
to the sudden application of too great cold, after being much 
enfeebled or rendered inirritable by the excessive heat of the sea- 
son, than to the too copious supply of water. On the contrary^ 
when plants have been too long exposed to a less stimulus of heat 
than natural or usual, the spirit of vegetation becomes accumu- 
lated ; and if they are suddenly subjected to much greater heat, 
their too great increase of action induces inflammation, and conse- 
quent mortification and death — as occurs to those people who have 
had too much warmth applied to their frozen limbs. Experi- 
ments of this kind were instituted by Van Uslar. He increased 
the irritability of Euphorbia* jieplus and esula by secluding light 
and heat from them, and when he exposed them to a meridian 
sun they hecdimQ gangrenous, and died in a short time." 
In order, however, to bring the case quite home, I made this 
last experiment upon the potato-plant itself, in the following 
manner : — 
On the 27th of December, 1845, I had planted 14 sound po- 
tatoes, and four in various stages of disease, in pots, and placed 
them in a small vinery, slightly heated by tan. Every one grew, 
but the sound ones the most vigorously ; as may be seen by the 
accompanying specimens of their leaves. I never saw plants with 
more healthy foHage ; for the season was unusually mild, not a 
single frost, I believe, having occurred during January, and I had 
not stinted them of water. On the 21st ot March 1 selected the 
most flourishing plant from amongst them, and, having watered it 
thoroughly, set it at once in rather a dark corner of a dairy with 
a glazed window, which was closed at night and open by day — 
* Succulent plants. 
