212 FISHERIES OF THE UNITED STATES. [28] 



too deeply for the open edge of the shell to reach above the mud and 

 draw a constant supply of water and food onto the gills. The placing 

 of adult oysters upon such bottoms at convenient points to 'fatten' for 

 the market is a well-known practice. The oyster embryo would be in- 

 gulfed and smothered at once if it should settle down on such a bottom, 

 and in order to have the least chance of survival and long life the young- 

 oyster must find some solid substance to fasten itself to, in order to 

 preserve it from sinking in the soft mud or from being covered by shift- 

 ing sand or gravel. As soon as the\oung oyster finds such a solid body, 

 rough and clean, it fastens one valve of its shell to it by secreting a 

 cement of shelly matter around the growing edge. 



"The living and dead shells of the adult oysters furnish the best sur- 

 faces for the attachment of the young, and for this reason the points 

 where oyster beds are already established are those where the young 

 have the most favorable surroundings and the best chance for life, and 

 the beds thus tend to remain permanent and of substantially the same 

 size and shape. 



" The great mortality of the young, after they have fastened them- 

 selves to the shells of the adults, is due in part to want of room, in part 

 to the attacks of enemies, in part to accidents, such as the shifting of 

 the bottom, and in part, no doubt, to lack of food. While the supply 

 of organic matter which is carried to them by the water is very great, 

 it is not unlimited, and the amount which each oyster can obtain 

 at any one time is quite small, and if the oysters covered the bottom in 

 sufficient abundance, some of them might fail to obtain a sufficient sup- 

 ply. I do not believe, however, that this ever occurs, for long before 

 the oysters are sufficiently abundant to exhaust the supply of organic 

 matter, their numbers are limited by other conditions. The growth of 

 an animal does not depend upon the supply of food in general, but 

 upon the supply of the least abundant of the necessary ingredients of 

 the food. It is well known that a field that is very fertile will fail to 

 produce a satisfactory crop of a plant which needs some particular food- 

 ingredient which the soil contains in too small quantity. Although food 

 in general is very abundant, the growth of this particular crop depends 

 upon the amount of this ingredient, and while the seed which has been 

 planted yields an abundant crop of young plants, only a few are able to 

 grow up, and these can grow no faster than they can extract this partic- 

 ular ingredient from the soil. 



" In addition to organic food, the oyster needs a supply of carbonate 

 of lime to make its shell, and this is supplied to it, in solution, in sea- 

 water. If the shell is thin, or if it is formed very slowly, the danger 

 from enemies and accidents is greatly increased ; and those oysters which 

 are able to construct their shells with the greatest rapidity are the oues 

 which survive and grow up. The amount of dissolved carbonate of 

 lime which the ocean contains is unlimited, but the amount which can 

 reach each oyster is not very great ; and if all the oysters which attach 



