EUROPEAN METHODS OF OYSTER-CULTURE. 
377 
Mobius lias, furthermore, supported his view that physical conditions have limited 
and will limit the size of the Holstein banks, by adducing the matter of percentage of 
increase. This he has determined by comparison of the number of oysters as fished 
from the banks to be about 421 u half-grown” to 1,000 “full-grown” oysters. This 
proportion, it will be admitted, determines the natural increase of the banks, but it 
can obviously have little to do with proving that artificial production in the neigh- 
borhood of the natural banks would be unsuccessful. The French culturist, on the 
other hand, might well suggest that this proportion of natural increase is a large 
one, since in French regions most favorable for artificial production the banks, so far 
from increasing, retain with the greatest difficulty the average number of spawning 
oysters. 
The third reason given by Mobius for lack of German success in French cultural 
methods is the coldness of the northern winter and the severity of storms, often 
occurring when the tide is at its lowest ph ise. It is certain, as Prof. Hoek pointed 
out to the writer during a visit at the Helder, that the German coast is not far distant 
from the northern limit of the oyster, and that its natural increase, therefore, is less 
favorably conditioned. The dangers of the Holstein bank to direct freezing in winter, 
as Mobius has stated, may well be regarded on every side as formidable, especially in 
artificial production, where young oysters affixed to the collectors are to be retained 
during the winter. These dangers would appear, however, to render success with 
French culture costly rather than impossible, necessitating the transfer of collectors 
to deeper water or to localities that have proven safe, or, as in Brittany, providing 
special reservoirs for winter storage. 
That natural banks exist even in great number in the Wattenmeer, and that the 
Danish banks, which are located considerably to the northward, appear to bear the 
cold and storms of rigorous winters with more or less success, seem to suggest that 
a provision for safely wintering oysters, even in the youngest stages, might not prove 
an impossible task. Indeed, if a good set of oysters were obtained in the German 
sea by the introduction of improved collecting methods, the use of suitable reservoirs, 
as those of the government station at Husum, which serve every year to harbor the 
marketable oysters during the coldest weather, might well be expected to provide 
safe winter quarters for the young. 
The reservoir at Husum (PI. lxxviii, Fig. 2) is admirably devised and merits at 
this point a brief discussion. It was placed at Husum on account of transportation 
facilities, although its situation is in many regards unfavorable. Husum, as already 
noted, is at the southernmost corner of the Wattenmeer, probably at one of its most 
muddy shore points, and its low, rich meadows are strongly protected against storm 
tides by heavy fringing dikes. These, by an indentation, allow a wide canal to carry 
freshened water seaward, and thus provide a harbor for the fishing vessels of the 
little port. The slanting sides of this canal are of the softest mud, reminding one of 
the great canal at La Tremblade. Its waters, which become almost as salt as the 
outer Wattenmeer at high tide,* are allowed to pass through a sluiceway into the 
neighboring government reservoir. The fall of tide, averaging about 10 feet, is suf- 
ficient to allow the basins to be emptied daily. 
At low tide (July, 1892) 59° 1.013, at high tide 1.0235. 
