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naked eye. Cut a potato in two through its root stem; trim the surface so 
that some of its eyes will be in section; coat the surface with a solution 
of bichromate of potash; dry the surface with filtering-paper, then coat 
it all over several times with a strong alcoholic solution of iodine; the 
starch will become stained of a dark blue, while the vascular bundles 
will remain yellow. An examination will show that the air-ducts ex- 
tend in every case to. the eyes. 
The stalks being simply an extension of them, 2 and 35 3 represent the 
combination of the spiral and dotted ducts; A, the root stem; B,a new 
growth or tuber from 1. Viewing their connection in this way, it will 
be seen that any germinal disease entering through the root-stem A will 
necessarily communicate through all the connecting links, viz: A, 2,3 3, 
B. In my former paper on this subject, published in the monthly report 
alluded to, Fig. 22, page 508, represents a sectional drawing of the air- 
cells, showing their general character; SS represents the fruit of a 
slender light-colored myceleum, which I have found traversing the ex- 
terior and interior of the withered potato-stalks. In the more advanced 
stages the fruit has appendages in length about one and a half times the 
diameter of their seed-bags,S 8. They have a thorn-like appearance, 
slightly wavy, and of amber color. To the naked eye they appear like 
fly-spots, and are very numerous. The conceptacles appear black, but 
when treated by nitric acid the dark color is removed and a cellular un- 
der surface of an amber color is exhibited. Thus far I have not been 
able to detect any sporangia in them. This may be accounted for from 
the fact that all the specimens I have examined had been dried up for 
a long period. 4 represents the fruit of Peronospora infestans on the 
leaves very highly magnified. The arrows represent the movements of 
the fungus matter; C, starch-cells, liberated by the fungoid solution . 
and full of starch granules; D, the starch-cells of watery potatoes. 
They contain very little starch. HE, the starch-cells as arranged in the 
potato. Some are void of starch, while some are well filled; others par- 
tially so. H represents the condition of starch in water when a fresh 
potato is grated down, or when the cellulose-cells are rotted away by 
fungus, as in the case stated. 
The following mode of separating the vascular bundles from the pota- 
toes, so that they may be viewed separately, will prove of interest to 
the vegetable physiologist: 
Take a potato of medium size, remove the skin carefully without 
cutting the eyes; place it in a solution of sugar and water, (in the pro- 
portion of about two ounces of sugar to a pint of water,) and subject it 
to 75° EF. for about twelve days. The fungus of fermentation will re- 
duce the potato to a pulp, but the vascular bundles will be found apart 
and may be removed with a glass rod, and mounted in the usual way 
with gum or balsam. Under a power of about 100 diameters, they pre- 
Sent a most singular, yet beautiful appearance. The pointed forms 
which extend to the eyes may be distinctly seen. This experiment is 
most successfully performed with the eastern and western potatoes. The 
starch-cells of the Santa Fé potatoes, for example, remain in a compact 
form, even when the nitrogenous matter has been destroyed by fungus 
or infusorials. The “air bundles,” therefore, cannot be removed from 
them easily, which I consider another proof of their matured condition. 
The following chemical direct mode of making observations of the 
position and structure of the air passages I sometimes employ: First, 
remove from a healthy potato a thin slice or disk. Pour over it con- 
centrated nitric, muriatic, or dilute sulphuric acid, (caustic potash or 
soda will have the same effect,) when the starch will become transparent. 
