56 



littorea, to combat the growth of " bouquet ", quoting the 

 success attending the employment of this measure in the 

 ciaires of Sable-d'Olonne. Chondria and Hypnea appear 

 in summer and disappear in winter. 



The green filaments of Enteromorpha and Cladophora, 

 constituting the " Union vert " or green mud of the 

 Arcachonnais parkers, are the important smothering 

 alga; of this district, enwrapping the oysters in a dense 

 green blanket under the action of brisk currents or rough 

 weather. 



The common brown wrack Fucus vesiculosns grows 

 luxuriantly on the boundary palisades and on the 

 pointed stakes employed against predatory fishes and 

 contributes appreciably to the deposit upon the parks 

 of mud and sand from suspension in the water ; on 

 the other hand, the damp fronds of this wrack form an 

 excellent material in which to pack oysters for despatch 

 by rail. 



The tanole of delicate filaments characterisino- the 

 growth habit of the green conferva Vaucheria thuretii, 

 is a much more serious danger. This "cat's hair" of 

 the parkers penetrates the muddy bottom of the ciaires 

 to some depth with a net-work of threads retaining and 

 fixing sediment as it settles to the bottom. In this 

 way it tends to raise the level of the mud in the parks 

 and so cause deterioration of the surface. This obliges 

 the parkers to incur considerable and frequently recur- 

 ring expenditure upon the removal of the mud and sand 

 thus accumulated. 



Sea-grass (Zosiera) and the wrack above mentioned 

 (/\ vesiculosns) are occasionally uprooted in qreat 

 quantities by storms and thrown within the parks ; unless 

 removed quickly their decomposition is said to cause 

 serious losses. 



Diseases. — In addition to the many visible enemies 

 from which the parker has to guard his beds of oysters, 

 other malignant influences, more subtle, less easily recog- 

 nized, and more difficult to combat, occasionally appear 



