IN THE UNITED KINGDOM AND FRANCE, 41 



The long wet weed is found to form an admirable protection from 

 the sun. In fig. 20 the tiles it will be noticed are placed on a slope ; 

 this is found advantageous in a strong current. When the tide runs 

 for a long time in one direction, as in some rivers, and when the 

 water is more or less muddy at times, the mud deposits on the back 

 of the tiles, and the spat attaches on the other side. Fig. 2 1 is more 

 applicable where the flow is equal, and where as much mud is 

 likely to be deposited by the ebb as the flood tide. The other 

 methods given in figs. 22 and 23 are employed indifferently in still 

 waters, as in creeks, &c, and in open water, mud banks, weed beds, 

 &c, in harbours. 



For sketches of one of the imperial pares at Arcachon, see plates 

 4 and 5, Appendix. 



The tank system of oyster culture in reality differs little from 

 that already described, as far as the placing of collectors and 

 oysters is concerned. The fault of many existing oyster ponds, 

 more particularly in Ireland is, that they are too small in area, 

 and not deep enough. The larger they are, within reasonable 

 bounds, the better and more natural they will be for the oysters. 

 From three or four acres to ten or twelve is the most useful and 

 most manageable size, while they should not be less than three feet 

 deep, and should vary to the depth of ten or twelve feet. The 

 water should have free access every tide, save during the spatting 

 of the oysters, when no water should be allowed to escape lest the 

 spat escape with it. But in very hot seasons considerable evapo- 

 ration takes place, more particularly in small ponds, and this causes 

 a good deal of disturbance in the density of the water, which is 

 prejudicial. This therefore should be carefully watched, and 

 should it threaten to become dangerous, it will be advisable to let 

 in a portion of fresh water if possible. 



Weeds are often very troublesome in tanks or ponds, more par- 

 ticularly the green filmy weed " cladophera," known commonly as 

 " blanket-weed." This is very dangerous to the oysters, and 

 means should be taken to remove it. 



It is usual in ponds to gravel large portions of the bottom in 

 order that provision may be made to catch that portion of the 

 spat which fails to adhere to the collectors, and the shortest time 

 before spatting that this gravel is cast in the better for its clean- 

 liness. Hurdles and fascines however have been found to answer 

 well in such places, and as a large number of collectors is 

 required, they will be found much cheaper. Engravings of 

 hurdles, fascines, &c, are appended, and the method of fixing 

 them is shown also (see plate 6). They are fixed in rows by 

 means of pegs, about two or three feet above the oysters, 

 which are scattered on the soil under them, as shown in the 

 engraving, though of course much more plentifully than they 

 are therein depicted. Furze bushes are also found to answer 

 fairly, and are cheap ; but fascines and bushes are scarcely so suit- 

 able in a tideway in consequence of the liability of the twigs to 

 catch weed, break, and float away, when the spat is carried with 

 them. In all cases when wood is employed for collectors, it should 

 be dry, hard, and sapless, and cut at least in the preceding season. 



Oysters are more easily detached from wood collectors; the 



