ments are none of them peculiar to particular species; several of 
them are often combined in one. A free swimming on the surface, 
like that of diatoms, was never observed. 
The first two of these movements depend on the formation, 
during the motion, of a filament of mucilage, by which the des- 
mid is attached to the bottom; the gradual lengthening of this 
filament, by the formation of fresh mucilage, causes the desmid to 
rise. The filament is best detected by a weak solution of methyl- 
violet or fuchsin, which does not kill the desmid. Cyanin also 
answers, but not so well. Other pigments do not stain it, Many 
species of Euastrum, Cosmarium, Staurastrum and Pleurotenium 
exhibit the same phenomenon. The greatest length of filament 
observed was 3™™; the most rapid motion, in Clostertum acero- 
sum, 112" in 30 sec.; many species are quite motionless. Light 
exercises an influence on the direction of the movement similar 
to that of zodspores, but not on its rapidity. The elevation and 
depression appear to be independent of the direction of gravita- 
The author considers the cause of the motion to be the exuda- 
tion of mucilage, which does not take place simultaneously and 
uniformly over the whole surface of the desmid. This formation 
of mucilage is not the result of disintegration of the cell-wall 
itself; it proceeds directly from the cytoplasm and passes through 
the cell-wall without the latter undergoing any change. Many 
species are completely surrounded by a gelatinous envelope, 
while others are comparatively free—A. W. Bennett, London. 
PLEOMORPHISM OF AtGa&.—Dr. A. Hanszig publishes in the 
Botanisches Centralolatt an elaborate paper which has for its object 
to prove that a large number of algz hitherto referred to the 
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ae together by insensible gradations. Thus we may have one and 
-the sam 3a occurring in its mature form, and in its Stigonema, 
Leptothrix, unicellular, Nostoc, Ulothrix, and a variety of other 
ugl h i 
forms. Euglena he regards also as genetically connected with 
new analogy between the Schizomycetes and Schizophyce® by 
the discovery of a motile organism which he names Chroomonas 
_ nordstedtii, and which he regards as the swarm-cell condition of 
a phycochromaceous alga, probably an Oscillaria—-A. W. Benneth 
TREE GROWTH ON THE PLains—From a recent paper on “Tree 
Planting on the Plains,” by Robert W. Furnas, we extract the 
_ following statistics of the growth of trees, as shown by actual 
380 i | General Notes. [ April, 
\ 
