380) REPORT OF COMMISSIONER OF FISH AND FISHERIES. 
The idea is commonly held that the soft organic mud on the oyster | 
beds stimulates the growth of diatoms, but a microscopic examination 
of specimens of mud taken from different oyster beds revealed the fact 
that they were apparently not more numerous in such places than on — 
the sandy bottoms similarly situated, provided that they were contin- 
ually covered with water. On the other hand, those muddy places | 
which are left dry between the tides were found to be much richer in 
diatoms than similar sandy places. The species living on the bottom 
apparently differed from the pelagic ones, but their presence in the 
stomachs examined indicates that they also served the oyster for food. 
These observations were made at places where the current was strong. 
They do not, therefore, by any means preclude the possibility that in — 
stagnant or slowly flowing water muddy banks may form a much 
better soil for diatoms than sandy ones. The fact that they are more 
numerous on muddy bottoms near the shore which are left uncovered 
by the tide even indicates this. We might account for the facts above 
stated by supposing that the diatoms are swept along so fast by the 
strong currents that they have not time to settle on these mudbanks, 
and might perhaps also thus explain the controversy between oyster- 
growers as to whether muddy or sandy bottoms furnish the most favor- — 
able places for planting. That sand is sometimes preferable we learn — 
from the following quotation from Professor Brooks’s oyster report. 
Within the harbor, for instance, considerable ‘“‘muddy bottom has 
been utilized by first paving it with coarse beach sand. No spot where 
there is not a swift current is considered worth this trouble.” 
This, of course, is in complete harmony with our facts, since the 
stronger the current the more food that is offered. That there is an 
abundant food supply for oysters en sandy bottom is proved by the 
fact that the clams, living upon the same food as the ovsters. are often 
found on pure sand flats. 
The fact that the mud bank, on microscopic examination, did not 
prove to contain more diatoms than the sand did not seem to furnish 
sufficient evidence on which to base an opinion as to the stimulating 
power of the mud on the growth of diatoms, as this might possibly be 
perceptible in the greater quantity of diatoms in the water above. To 
determine this, diatoms were collected from the water over mud banks 
and also from over pure sand and the results compared, but no per- 
ceptible difference could be detected. The instrument used for this 
purpose was a Miiller’s net secured firmly by means of two strong 
wooden poles to the dredge in such a way that it was immovable. The 
poles “A” are of strong wood. Two incisions are made in these, extend- 
ing about half way through the wood at the points a and b in such a 
manner that the iron bars D of the dredge fit perfectly in them. A 
erosspiece C is now screwed on, so as to retain the poles at an angle of 
about 45° with the bottom when the dredge is lying on it. The net is 
fastened between the poles near the top, the ring fitting into incisions 
in either side, enough space being allowed between them and the top 
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