A BOTANICAL -EXCURSION IN MY OFFICE. sly 
chia; 29, Arachnoidiscus; 30, Grammatophora; 381, Biddulphia,—a, 
two frustules, still enclosed by the ‘‘ connecting membranes,” b, ‘‘ con- 
necting membrane,” widening previous to self-division; 32, Pleuro- 
sigma; 83, Synedra; 34, Coscinodiscus; 35, Triceratium; 36, Amphi- 
tetras. 
The forms are not accurately drawn to scale, but are for the most 
part magnified about four hundred diameters. 
eee eens 
A BOTANICAL EXCURSION IN MY OFFICE. 
BY PROF. HORATIO C. WOOD, JR., M. D. 
PROBABLY most of the readers of the NATURALIST have, 
at some time or other in the last five years, owned, or at 
least been interested in aquaria. If what happens in 
Philadelphia may be’ taken as an index, many such ob- 
servers of water-life have been pestered by a minute 
growth, which seems to flourish alike on plant or stick, 
on the living and dead. Last winter and spring the 
writer of this article had a small aquarium, which, as 
far as plants were concerned, was stocked chiefly with the 
Ceratophyllum, or hornwort, which, as is well known, 
possesses a vast abundance of finely dissected, twig-like 
leaves. Glancing one day at his water-garden, he 
noticed on these little cylindrical divisions a fine hazy 
fringe, scarcely to be perceived except by allowing the 
light to shine through the vessel containing the plant. 
Now this fringe, this nebulous garment clothing the horn- 
wort, was the minute growth alluded to, which, though 
not strictly parasitic, not feeding on the plant to which it 
is attached, is, in most cases at least, associated with a 
sickly state of the larger plants, and certainly detracts 
om their beauty when viewed with the unaided eye, as 
in aquaria. But let us take our forceps, break off -one 
