58 
ments which accompany the specimens exhibited in mass are de- 
signed to give the visiting public some idea of how these lowly 
organized plants look when viewed under certain degrees of 
magnification. The photographs of the diatoms illustrate not 
only the elegance and symmetry of form of these microscopic 
organisms, but also the beauty, regularity, and delicacy of the 
oie ring which characterizes the siliceous shells of these 
nute one-celled plants. There are exhibited also samples of di- 
atomaceous earths, which form extensive deposits in various parts 
of the world and consist almost wholly of the cen shell-like or 
box-like cell-walls of diatoms. These diatomaceous earths 
sometimes soft and powdery but are often hard and rock like 
They are put to various economic uses, one of the principal be- 
ing as an ingredient of polishing powders and scouring com- 
pounds. The minute flinty boxes constituting the shells of dia- 
toms are brittle but their fragments are very hard and are well 
adapted for polishing stones, metals, etc 
The second museum case of the series contains some of the 
green algae, the group which includes the lower plants that are 
sometimes called the pond-scums, green slimes, green felts, green 
seaweeds, stoneworts, etc. Some of these are microscopic an 
the enlarged figures and drawings which accompany the speci- 
mens or are substituted for them, are therefore as a rule much 
more instructive to the visitor than are the specimens themselves. 
However, some of the green seaweeds attain a considerable size 
and begin to look a little more like what are popularly termed 
‘plants.”” The Caulerpas, for example, — natives of the warmer 
seas — sometimes get to be three or four feet long, though the 
genus, as at present generally accepted, includes a wide range 
both of form and of size, The genus Caulerpa is represented 
in the public show cases by several species, illustrating the 
principal subdivisions of the group. Among the green sea- 
weeds a curious plant that is always among the first to attract 
attention is Pemicil/lus, sometimes called also the ‘‘merman’s 
shaving-brush” from its very patent resemblance to certain forms 
of brushes. The most common species, Penicillus capitatus, 
grows in peamida: southern Florida, and the West Indies, for 
