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MICROSCOPIC OBSERVATIONS. 
By Tuomas TAyLor. 
POTATO BLIGHT AND ROT.—Some eminent chemists, such as Dr. 
Lyon Playfair, believe that the potato-plant, when healthy, is not sub- 
ject to attacks from fungi. Ina lecture delivered by him before the 
Royal Agricultural Society of England, December 9, 1845, he remarked 
that ‘‘ much had been said and written with regard to the source of the 
disease, and since minute fungi had been assigned as its cause, potatoes, 
apples, and other fruits had been inoculated with fungus spores, and 
had become diseased; but if there were not some previous disease in . 
the potato itself, how was it that some varieties of potatoes escaped 
while growing in the immediate vicinity, while others were attacked ?” 
The disease, he believed, arose from structural or chemical causes. 
When a decayed potato was examined it was found that the diseased 
spots were always in the region of the spiral vessels, whose function it 
was to carry air into the tissue of the plants. He believed the dis- 
ease originated in the oxidation of the tissue. The Rey. M. J. Berkley, 
the leading mycologist of England, on the other hand, contends that the 
fungus Botrytis infestans, or, as now classed under the new genus, Pero- 
nospora infestans, will attack the healthy tubers; but the question 
arises just at this point, what means have we of ascertaining the per- 
fectly healthy structure and chemical state of tubers? Every farmer 
plants what he deems sound tubers, yet, in the majority of cases, since 
1845, the crop during very moist seasons has been more generally 
affected than it was prior to that date. 
The severity of attacks of fungion plants will depend in some cases on 
the density of their organic structure and the solubility of their nitro- 
genous matter. The nitrogenous principle of potatoes, for example, is 
soluble in water, that of turnips nearly insoluble. The former, therefore, 
ferments more readily than the latter. The leaves of a healthy peach- 
tree, when placed in a moist atmosphere at about 75° F., resist fungoid 
fermentation for months, while those of a peach-tree affected with the 
‘ vellows,” placed under the same general conditions, will quickly fer- 
ment and become covered with the fruit of the fungus mucor. The first 
possess an antiseptic property, the second are deficient init. If two 
blocks of wood, one of boxwood, the other of pine, are placed in a fun- 
goid solution, the first will resist the action of the mycelium because of 
its density, while the second will quickly decay. The first absorbs a 
great deal of water, the second very little. A certain amount of moist- 
ure, and sometimes of water, is necessary to the growth of fungi. 
In years previous to the noted potato-rot of 1845, the average amount 
of water found in healthy potatoes, according to Professor Playfair, was 
72 per cent. That of unhealthy tubers since that date, 80 per cent. 
The tendency to ferment is therefore increased. It was observed by 
Professor Playfair, in his lectuye alluded to, that a peculiar state of the 
weather had been observed all over the north of Europe where the 
disease had been seen, as well asin America. The widespread use of 
the potato as an article of diet, especially among the laboring classes 
throughout Europe, must have Jed to the extensive planting of diseased 
potatoes in 1846, because healthy seed could not be found. Indeed, 
Professor Playfair, in his second lecture of the 10th December, 1845, 
recommends “the planting of diseased pctatoes as seed rather than 
none.” He further states that there was no prospect of obtaining 
