[5] CAUSE OF THE GREENING OF OYSTERS. 797 



to establish some experimental parks on the Croisic. After some months 

 of study to determine the elevation of the grounds and their nature, I 

 arranged an experimental j^ark on the shore, and I sought to imitate 

 the method practiced along the shores of the Seudre. The claires which 

 I had establisbed at Sissable were placed in such a condition as to fit 

 them to receive the water, each spring tide, during 10 to 12 hours or 

 less. Situated on the eastern part of the Croisic, where the sea is never 

 disturbed by heavy waves, was the ground which I had at my disposal, 

 and under such conditions that the methods in use at Marenues and on 

 the Tremblade could be put into operation. 



I will not speak here of the results of these attempts. They have ex- 

 ceeded my expectations. The products grown at Sissable would seem 

 to rival those of Marennes, and if they are not yet well known it is be- 

 cause the establishment "where they are grown has not yet i^assed far 

 beyond the experimental stage, having as yet yielded for consumption 

 only from 100,000 to 150,000 oysters. The product will, besides, always 

 be as limited as the grounds (parks) where they are reared. 



Besides their other qualities, in which, as I have said, they approach 

 those of Marennes, the oysters of Sissable acquire a higher degree of 

 viridity than those grown in the claires on the Seudre. I therefore found 

 myself in the presence of the problem of which I will treat in this notice, 

 and which I determined to solve. 



Like Gaillon, of whose researches I was ignorant at this time, as well 

 as of the publication of M. P. Petit, which appeared after my observa- 

 tions, I remarked the relation which existed between the viridity of the 

 claires and that of the oysters. 



The material which coats the bottom of the claires forms a slimy, 

 blackish green layer, and superficially has all the appearance of being 

 composed of Nostocacece, an inferior group of Algae, representatives of 

 which are so frequently found at the bases of humid walls, in ditches, 

 and marshy places. Upon microscopic examination", M. Bornet and 

 myself recognized that this substance was composed of an alga belong- 

 ing to an entirely diiferent group, in fact, of diatoms, the innumerable 

 fusiform frustules of which traversed the field of the microscope in all 

 directions in a very lively manner. We also thought that we recog- 

 nized this diatom as nearly allied to Amphipleura and Navicula. But 

 finally, in order to have the determination made as exactly as possible, 

 we submitted it to M. Grunow, the able Austrian algologist, who very 

 willingly examined it, stating that it was a variety of his JS^avicula 

 fusifonnis, to which he had given the name of ostrearia. (Grunow ; 

 New Di.itoms from Honduras, in Month. Mic. Journ., 1877, p. 178.) 



Explanation of Figure 1. 



Havicula fusifonnis, var. ostrearia, Grunow. 



Enlarged 330 times. (The densely stippled extremities of the frustules 

 indicate the portions ol; the organism in which the blue vegetable pig- 

 ment is contained.) 



