380 REPORT OP COMMISSIONER OF FISH AND FISHERIES. 



The idea is cominouly held tliat the soft organic mud on the oyster 

 beds stimulates the growth of diatoms, but a microscopic examination 

 of specimens of mud taken from different oj-sterbeds 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 i)elagic 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 i^ossibility 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 j^referable 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 on sandy bottom is proved by the 

 fact that the clams, living upon the same food as the o^'^sters. 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 h in such a 

 manner that the iron bars D of the dredge fit perfectly in them. A 

 crosspiece 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 



