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POPULAR SCIENCE REVIEW. 
11 decidedly different.” I have been unable to infect the potato plant with 
the Pythium or the Equisetum with my potato oospores. My experiments, 
therefore, agree with the results obtained by Dr. Sadebeck, and the two para- 
sites may be considered different. 
The Black Knot of Plum and Cherry-trees is the subject of an important 
memoir, illustrated by plates, in the u Bulletin of the Harvard University.” 
The paper is illustrated by three beautiful plates, showing this disease in 
various stages, and the whole structure, development, and fructification of 
Sphoria mortosa of Schucinitz, the fungus which produces this black knot, 
which so deforms and injures plum and cherry-trees throughout the 
Northern States and Canada. The remedy is the knife or the axe. For 
prevention Dr. Farlow recommends the extirpation of choke cherry-trees, 
upon which the pest largely breeds in the vicinity of Boston. Farther west 
it would all the more be necessary to destroy all the wild plum-trees 
( Prunus Americana ), which are fearfully infested. 
Mr. Meehan's Explanation of his Attack on Mr. Darwin. — At a recent 
meeting of the Academy of Philadelphia Mr. Thomas Meehan remarked 
that the American correspondent of “Nature” had characterised some 
recent remarks of his on fertilization by insect agency as an attack on 
Mr. Darwin. He thought the members of the Academy would bear him 
out in the statement that the facts and observations he had from time to 
time offered were submitted in no spirit of antagonism to Mr. Darwin, but 
often favoured as much as they opposed views held by that distinguished 
gentleman. Even those who were avowed partisans of Mr. Darwin felt it 
necessary to strengthen their position by searching for new facts. Surely 
the mere student, who was willing to wait till the evidence was all in, 
might offer the facts as he found them, without being liable to the charge 
of direct antagonism. 
CHEMISTRY. 
Detection of Chicory in Coffee . — Professor Wittstein, who has a long paper 
on the adulteration of coffee in the “ Chemical News ” (May 12), states that 
Mr. J. Horsley, some time ago, proposed the following process for the detec- 
tion of chicory in coffee: — If to a much diluted decoction of chicory a 
solution of bichromate of potash be added, no sensible reaction will take 
place. If, however, we subject to this same reagent a decoction of pure 
coffee, its colour will immediately darken, and become brown similar to 
porter. This is, therefore, an easy method of distinguishing between the 
two, provided they are separate. In mixtures the determination of the im- 
purity becomes much more difficult. In this case a dilute decoction is made 
of a weighed quantity of the suspected mixture. It is then to be heated to 
boiling and treated with the solution of bichromate of potash. A few 
decigrammes of copper sulphate are next added, and the solution is again 
to be boiled, whereupon a dark brown flocculent precipitate will be formed. 
The depth of its colour depends on the quantity of coffee in the mixture ; and 
we have thus, by comparing this precipitate with a similar one of the same 
