SCHULTZE, ON DIATOMACE.®. 17 
plant-cell to the Noctiluca, only represents the most external 
layer of the proto-plasm) is of the nature of clear albumen ; 
this also appears not to be wanting m Coscinodiscus, though 
in it covered by the siliceous coat, as itis m most plant- 
cells by one of cellulose. The currents of granules are also 
perfectly similar to those found in the extended threads of 
Gromiz, Polythalamiz, and Polycystinie. Unger has briefly 
(‘ Anatomie und Physiologie der Pflanzen,’ 1855, p. 282)—a 
view previously more specially propounded by Cohn (‘ Nach- 
trage zur Naturgeschichte des Protococcus pluvialis, Aus d. 
Leopoldinischen Akademie-Shriften)—classed together the 
currents in the fluid contents of plant-cells (2 8), the hairs on 
the filaments of Tradescaniia, with the phenomena presented 
by the threads of Ameba porrista, or the Polythalamiz, as 
I describe them, and the movements of the protoplasm he 
declares are exactly similar to those of the so-called sarcode 
of the Rhizopoda. I have compared the frequently described 
phenomena in the hairs on the filaments of Tradescantia 
with the currents in the Diatoms, as well as in the threads 
of the Rhizopoda, and must acknowledge their great simi- 
larity. I chose for the observation Tradescantia procumbens, 
the hairs of whose filaments present very transparent cell- 
walls and entirely colourless contents; the latter, in Tr. 
zebrina, for instance, being more or less real, detracts some- 
what from the distinctness of the movement phenomena. 
In the former, also, the granules are larger, and the material 
of the threads apparently more homogeneous. From the layer 
of protoplasm enveloping the nucleus proceed several thicker 
or thinner threads, traversing the cell im all directions, more 
frequently, however, lying close to the cell-wall (as in Rfi- 
zosolenia). They consist clearly of a basic material, with 
strongly refracting granules imbedded in it. The latter flow 
in the interior, or, as it were, on the surface of the threads, 
either in one direction only, or in opposite directions at the 
same time in one and the same thread, as may not unfre- 
quently be observed. In the broadest threads this double 
direction of the current is nearly universal, but it occurs also 
in the finest, which are almost imperceptible. The granules 
generally pass by each other undisturbed, or it may happen 
that one is taken back by the others—a proof that the double 
direction of the stream is not due to two separate threads. 
Individuals flowing quickly overtake others going more slowly 
in the same thread, and may then, as I once saw, suddenly 
turn back and proceed in company. The threads divide 
themselves frequently in a forked manner, and a granule 
reaching the point of division stops before committing itself 
