Diatomacee. 49 
and it led toa further examination of some fine scum—not 
Waddon scum, there is too much there for the purpose, but 
scum from undergrowths placed in glasses of water—and it 
also led to the discovery of two kinds of cells. These were 
carefully tended and watched; and, in a short time, two other 
bodies appeared in considerable numbers, one kind having the 
appearance of spores, beautifully bright, with a faint tinge of 
green; the other, by far the most numerous, rapidly moving 
animalcule-like creatures, colourless, and so exceedingly 
minute that with a }-power and number 2 eyepiece, nothing 
could be made of them. They swarmed in large numbers round 
the cells and ultimately disappeared. The whole phenomenon 
was analogous to what takes place in the germ frond of the 
fern. The germ frond of a fern is produced by a spore, and 
the what I take to be spores or z66spores in question, in a 
very short time settled down, and formed around them ina 
plane, a coherent, nearly transparent mucous frond, in which 
could be seen the new forms like in all respects their parents, 
the diatoms. 
Now, as regards these cells. Are they both produced 
from the same granular particle as in the fern, or does 
the fertiliser reside in a different looking plant as in some 
other vegetable forms? Permit me to call your attention to a 
matter of singular interest. I said that the diatom might be 
found on all water plants. Thereis an exception, and a most 
remarkable one it is. I don’t remember to have seen a single 
gathering that did not contain specimens of some members of 
the Oscillatoriacece, and not one of them has had a diatom. 
These consist of tubular filaments which have movements analo- 
gous to those of the diatom. They are always associated with 
the diatom, and without the diatom appear to be very busy in 
the manufacture of flint. With the diatom, although some 
nodules are produced, the plants flourish ; without it, they be- 
come weaker and weaker. I commend this part of the subject 
to your consideration; one pairof eyes is hardly sufficient for it. 
The silicious covering of the cell, however, is the chief object 
of interest to microscopists. Nothing is more beautiful. I shall 
say nothing whatever as to its perfection of form or the beauty 
of its striae and dots. You will find these all fully described 
in such excellent works as Carpenter's, Smith’s, and others ; 
but it is necessary to dwell for a few moments on its structure. 
It is composed of silica secreted from the water. The 
contents of this box forty years ago were in the chalk hills. 
Water percolated from the chalk through an artificial 
. obstruction, where evaporation was going on to a great 
extent, and the obstruction became enamelled with what 
we have here,—flint deposited from the water. This 
B 4 
