THE OYSTER AND THE OYSTER INDUSTRY. 35 



ing thorn directly from the beds. In many places the larger planters 

 buy of the "natural growthers", since steam vessels and heavy 

 dredges, such as are owned by the large oyster companies, are not 

 allowed to work on the natural beds. The "natural growther, " 

 with less capital, can afford to maintain a vessel and some hand 

 dredges and profitably sell to the large oyster company, which in 

 turn obtains seed more cheaply than it could by supporting its own 

 sailing vessels and crews. In States where such a system is prac- 

 ticed, the natural beds are set aside by the State for the" " natural 

 growther" with limited capital. 



The material dredged from the natural beds usually contains old 

 shells, rocks, and debris, in addition to the oysters. Sometimes the 

 whole is bought at a reduced price, but usually the desirable material 

 is culled out and the clustered oysters broken apart as far as possible. 



Wafer. — As a general rule seed oysters should not be obtained 

 from warm waters and put down in those excessively colder. If 

 this be done, it will usually be found that their growth is checked 

 for some time and that a certain percentage die. After a time, 

 however, they become accustomed to the reduced temperature and 

 renew their growth. 



In general, the warmer the water the more rapid the growth of 

 the oysters. This is due both to the greater al)undance of food 

 material and to the fact that the bodily activities of the oyster 

 proceed more rapidly when the organism is warmed to a relatively 

 high temperature. 



The density of the water should be between 1.007 and 1.023. 

 Although oysters are found both in water of lesser and of greater 

 densities, they do best within the limits stated. 



Food. — The character of the food of the oyster is discussed on 

 page 19. In order to profit by planting oysters, a sufficient quantity 

 of food for them must be assured. Often certain waters and bottoms 

 are suitable for catching set on cultch, but do not possess a suffi- 

 cient food supply to enable the oysters to grow and fatten rapidly. 

 Other grounds furnish an abundant food supply, but the water is so 

 loaded with debris that cultch and set are soon covered. Hence in 

 many cases cultch beds are placed in waters of the former character, 

 and the set is caught and later transferred to waters containing more 

 food. 



Care must be exercised not to place more oysters on the ground 

 than can be supported by the supply of food present. On the 

 average a])Out 500 bushels of seed are sowed per acre. The food 

 content of the water varies greatly from place to place and from 

 time to time in the same place. It is affected to some extent by 

 the amount of material brought from the land by the streams and 

 rivers. This again is dependent on the rainfall. As previously 

 stated, diatoms make up a considerable part of the oyster's food 

 and diatom growth is affected by materials washed down from the 

 land. A period of excessive drought causes a falling off in the 

 diatom content of the water. 



It would be well if a systematic biological study could be made 



of the food content of the water over prospective oyster grounds. 



In order to do this samples of water of definite amounts should be 



strained through No. 20 silk bolting cloth and the number and 



35286°— 21 23 



