1896 THE MICROSCOPE. 117 



was not possible to determine them conclusively in all 

 cases. There were found, however, numerous diatoms, 

 fragments of (Edogonium, Gleocystis, Calothrix and 

 Urococcus, and in much larger quantity, plants of Siro- 

 siphon informe Kg. Pine pollen and fragments of coni- 

 ferous wood were also noted as common inclusions. The 

 body of the specimen was found to consist of a plant 

 which could not be satisfactorily determined. The ma- 

 terial was therefore referred to Dr. Farlow, who not only 

 confirmed the observations previously made, but ascer- 

 tained that the dominant species was Dicothrix gypsophila 

 (Ag.) B. & Flk. From the facts thus noted the inference 

 was drawn that the pebbles might be regarded as verita- 

 ble museums which would probably disclose some new 

 form each time a fresh examination was made. 



More recently some of these j)ebbles were sent to Mr. 

 E. Grove, of England, who in turn transferred them to 

 Mr. George Murray, of the British Museum. Mr. Grove 

 undertook the determination of the diatoms, and has 

 added considerably to our knowledge of the composition 

 of these curious communal growths, by the publication 

 of a list eml)racing 24 genera and 100 species and varie- 

 ties. This somewhat extensive diatomaceous flora is, 

 nevertheless, hardly to be regarded as playing any 

 special role in the formation of the pebbles beyond the 

 fact of simple association, a relation which is readily 

 understood when we recall the very universal distril)U- 

 tion of these minute organisms, and the readiness with 

 which they take up their abode in almost any situation. 



The larger forms of plants found in the pebble were 

 determined by Mr. Murray, who has given, in addition 

 to other figures, excellent drawings showing the general 

 external characteristics of the pebbles. His determina- 

 tion of the components showed that, " the predominating 

 kind was clearly a species of Schizothrix while mixed 



