PLANKTON OF THE GULF OF MAINE 
471 
and the many smaller forms, but even for Zostera time brings progressive decomposi- 
tion. After it has disintegrated to a fine dustlike state, further oxidization probably 
takes place more rapidly, particularly when it is suspended in the upper, more illu- 
minated water layers. Is it not reasonable, then, to think of such organic particles 
or aggregates of particles as foci around which diatoms can multiply, being nourished 
by the nitrogenous substances as these constantly go into solution, just as the weeds 
in our gardens thrive around the particles of manure or of nitrogenous fertilizers 
that are similarly disintegrating or dissolving in the soil? At any rate, whether or 
not this particular picture be correct, a vast supply of organic matter is derived from 
the Zostera, the constituents of which must eventually join the general nutritive 
store of the sea water in which it decays and from which it was taken in the first 
instance. Even such of it as passes through the digestive tracts of bottom-dwelling 
mollusks must also travel the same path in the end, either as excreta or by the final 
death and decay of the endless chain of animals that feed one on another. What is 
true of Zostera is equally true of the more rapidly decaying marine algae. 
Qualitatively, at least, all this applies as well to the Gulf of Maine as it does to the 
other side of the North Atlantic, Zostera, with the “rock weeds,” “kelps,” etc., 
being abundant, with the general conditions of temperature, etc., under which they 
live, die, and decay, much the same. And since Zostera forms dense fields in the sandy 
and muddy bottoms of sheltered bays, estuaries, etc., all around the coast from Cape 
Cod to Nova Scotia, with beds of “rock weeds” (Fucacese), Laminariae, etc., along 
the rocky or stony shores where it fails, the organic debris produced by the annual 
decay of submerged marine vegetation along the coast, spermophyle and algal, 
must reach very large proportions. 
The decay of the dead bodies of the members of the animal communities that 
thrive so abundantly in the gulf, both on the bottom and planktonic, are also con- 
stantly making nitrogenous compounds available in the first instance as detritus, 
finally to find their way into solution. The importance of the rain of dead bodies 
of planktonic organisms, which is constantly descending through the water, as 
providing pastures for animals living on the bottom below, has long been realized. 
Some are devoured by other animals en route; others, like the medusae and cteno- 
phores, may entirely decompose and go into solution as they sink; but it is probable 
that in moderate depths, such as those of the Gulf of Maine, fragments at least of 
most of them reach the bottom before they entirely disintegrate. Naturally a 
larger amount of plant detritus accumulates on bottom in shoal water near land 
than out at sea because nearer the source of supply, and animal debris may also be 
expected to be most abundant in moderate depths. Think, for instance, of the product 
of the death rate in an extensive mussel (Mytilus) bed. But the following analyses 
prove that there is some nitrogenous debris (derived from plants and animals com- 
bined) everywhere in the uppermost layer of mud, silt, or sand on the bottom of 
the gulf, in deep water as well as in shoal. 
