Natural History^ 167 



It microscopically, we found that the red tint was due to the pre- 

 sence of small spherical globules of a bright red colour, which 

 were surrounded by a gelatinous membrane, transparent, slightly 

 yellow, the size of which varied from three to six millimetres in 

 apparent diameter : in certain cases they were arranged in lines 

 representing fibres ; and they were mixed with fragments of moss 

 and dust detached from the rocks. 



A comparative observation was made on the deposit from the 

 water of the red snow of the north, brought by Captain Ross, of 

 which M. de CandoUe possessed a small quantity ; and it was found 

 that the globules in it were identical with those of the Alp snow ; 

 so that these spots must be due to the developement of this kind of 

 plant. M. de CandoUe, who has studied them closely, does not 

 view them as belonging to the Uredo, but rather as forming a new 

 genus. — Bib. Univ. xxvii. 132. 



3. Artificial Production of Pearls. — Mr. Gray whilst examining 

 a specimen of the shell Barhala Plicata, in the British Museum, 

 observed on it several very fine regular shaped semi-orbicular 

 pearls of most beautiful water, and afterwards on examining the 

 collection of pearls at the same place, he had an opportunity of 

 observing in one of them attached to a fragment of the same shell, 

 and cracked across, that it was formed of a thick coat consisting 

 of several concentric plates formed over a piece of mother-of-pearl 

 roughly filed into a plano-convex form like the top of a mother- 

 of-pearl button : the other pearls all appeared to be formed in the 

 same manner, and on some pieces of shell where the pearl had 

 been destroyed or cut out, there was left a circular cavity with a 

 flat base about the depth, or rather less, than the thickness of the 

 coat which covered the pearls ; proving that the pieces of mother- 

 of-pearl had been introduced when the shell was younger and 

 thinner, and that they must have been introduced between the 

 leaf of the mantle and the internal coat of the shell. 



Hence Mr. Gray was induced to expect that pearls of a very 

 beautiful appearance and form for setting might be obtained with 

 facility at home. He introduced similar pieces of mother-of-pearl 

 into the shell of the Anodonta Cygyieus and Unio Pictorum; this 

 was done without much difficulty, the valves of the shell being 

 forced open to a moderate breadth, retained so by a stop, the mantle 

 slightly turned down, and the pieces introduced to some little 

 distance by a stick ; the stop was then withdrawn, and the animals 

 returned to their natural habitation: of the thirty or forty pieces 

 introduced, only two were pushed out again, the rest being placed 

 by the animal in a convenient situation. In several afterwards 

 destroyed, they were found near the posterior slope of the shell, 

 where the pearls are situated in the barbala. 



This plan of forcing the production of pearls by fresh water 



