OYSTER-CULTURE IN FRANCE. 
379 
shell of glass, and contain a number of pellets of golden-brown coloring matter. An 
exceptional diatom, Amphipleura ostrearea (Gr.), contains a green pigment and is 
nowhere as abundant as at Marennes. The oyster feeding upon it, stores away, first in 
gills and then in mantle, the vegetable coloring. The green color is said by the con- 
noisseur to give the oyster an inimitable and exquisite flavor, as if savored with mush- 
room or truffle, an idea which the culturist, however skeptical, is not apt to refute. 
With a view to higher market price, he has even studied astutely how to give his 
products the maximum degree of color in the least time. He early attributed the 
cause of coloration to the myriads of green diatoms, which he termed u moss,” and 
discovered that this moss developed most readily in muddy basins where the water was 
seldom renewed. The low regions of swamp and salt meadow, often for a mile on either 
side of the Soudre, has now been built into claires , drawing water from intersecting 
canals (Plate lxxvii, Pig. 2). The claires nearer the river may readily renew their 
waters every few days, offering the better conditions for elevage. The claires situ- 
ated upon the uplands, where rapid greening takes place, can only be refilled a few 
days monthly, in accordance with the lunar tides, and their shallow stagnant waters 
are therefore most dangerous to the oysters. I am told that here the mortality may 
average 50 per cent, even though under favorable conditions the oysters will green in 
a fortnight. 
The claires at Marennes are established as follows: They are crowded together, 
separated only by low earthbanks, are small in size, the largest perhaps 75 by 100 
feet (Plate lxxviii, Fig. 1). The bottom is of soft, light-brown mud, banked up in the 
middle; the marginal trenches are deepest at side, draining into the canal. The drain- 
pipe piercing the low earthbank is usually a bored pine log, a foot in diameter. 
The drain- stoppers are like a mallet, removed conveniently from above by means of 
the handle. In the best development of the green moss the eleveurs believe that the 
claire bottom should, like a cultivated field, be annually broken and u freshened up.’ 7 
Early each spring, when the green moss is beginning to disappear, the ponds are 
emptied. After several weeks the bottom becomes seamed and cracked by the heat of 
the sun; the trenches are now deepened, the upturned soil so disposed as to give the 
bottom a mound-like appearance; the basin may even be spaded up as if for a flower 
bed. In August the water is again permitted to enter, at first but little at a time, 
allowing the crust to slowly deliquesce, a stage that often produces a froth-like 
appearance. A week later the claires are filled so as to allow about a foot of water to 
cover the*oysters. Late in August the green begins to appear, first in the low claires, 
then in the higher ones; in November it is at its height, the entire basin becoming 
literally moss-covered. Warmth is naturally essential to rapid greening, the shallow 
waters varying from 3° to 12° P. higher than margin of the Soudre (August 26 to 28). 
The slight freshening of water caused by the rains in September and October is also 
considered of advantage. Springs are absent. The differences in saltness of water 
of river, canal, low, and high claires , are certainly not marked — (73°) 1.023, (75°) 
1.0235, (76°) 1.0235, (80°) 1.021 to 1.0225. In value, adjacent claires, under apparently 
the same conditions, sometimes differ most unaccountably in the quantity of green 
moss that is produced, one claire often enabling the oysters to green thrice as rapidly 
as the adjoining one. For rapid greening it is found best to place the oysters not too 
thickly, a normal of fifty to the square yard. The oyster’s color may entirely disap- 
pear if the oyster is allowed to remain for a month or more in other waters, but is not 
