SPAWNING AND SETTING OP OYSTERS 
79 
It is possible that the diatoms sink into deep water when the water is warm and 
rise to the surface when the water is cooler; or else wind which cools the water also 
22 
MARCH APRIL 
2 4 6 8 10 12 14 18 18 20 22 24 26 28 50 I 3 5 7 9 II IS IS 17 19 21 23 28 27 29 
MAT JUNE 
JULY AUGUST 
Figure 18. — Charts showing the relative abundance of diatoms, taken with plankton net of No. 20 bolting 
silk, in Galveston Bay. Solid points represent collections in Offatts Bayou, each point being the average 
of three or more samples. Circles refer to collections in West Bay near Deer Islands, representing 
usually three samples in East Bay, near Hanna Reef, are designated by X’s. Abundance of diatoms 
was roughly estimated as follows: 0, none (although in no case were they considered to be absolutely 
absent) ; 1, very few; 2, few; 3, fair number; 4, many; 5, very many; 6, extremely abundant. The figures 
are only rough estimates but clearly show certain fluctuations, especially the disappearance of diatoms 
toward the end of the summer 
stirs up the diatoms which may have settled to the bottom ; that is, these minor vari- 
ations may have been due to the method of sampling, for the net was effective only 
for the surface 12 or 15 inches of water. \ It is this surface water, however, which is 
