M. Brongniart's Observations on Arborizations, i^c. 269 



Plantes, or in that of the Academic des Sciences. As to the 

 confervoid filaments, a great number of specimens present them, 

 which have the appearance of those figured by Daubenton ; but 

 we shall presently see what opinion is to be formed respecting 

 those alleged confcrvae. After Daubenton, Blumenbach, in a 

 letter to the Baron de Moll, of which an extract is inserted in 

 the Annals of Philosophy ♦, admits, that, although he had until 

 then rejected the presence of vegetables in calcedonies, he was 

 persuaded that these stones sometimes contain actual vegetables, 

 probably of the nature of confervse. He says he observed some 

 in specimens from Iceland and Catharinenburg, and adds, that, in 

 an agate which had belonged to a Japanese prince, he had re- 

 <;ognised the fructification of an unknown plant, having a consi- 

 derable resemblance to that of Sparganium erectum. This opi~ 

 nion, to which the name of so celebrated a naturalist might give 

 authority, has unfortunately never been farther developed by its 

 author, who has neither published a detailed description nor 

 figures of the vegetables which he thought lie had distinguished 

 in these calcedonies. 



The same opinion has been supported by Dr MacCulloch -f-, 

 who alleges that calcedonies contain arborizations of two kinds, 

 the one arising from the presence of vegetables, the other formed 

 by mineral infiltrations. He asserts that these two kinds may 

 be distinguished both by their external characters and by their 

 chemical nature, the former always becoming black when boiled 

 in sulphuric acid, while the others retain their original character, 

 and produce a slight effervescence. The same naturalist says he 

 sometimes observed articulations in these filaments ; but unfor- 

 tunately the figures which he has given of these objects are not 

 sufficiently enlarged, and are consequently insufiicient. If re- 

 ference be made to these figures, it is certainly difficult to refuse 

 admitting in some of them portions of vegetables even more com- 

 plicated than confervae, such as Jungermanniae. But these in- 

 filtrations sometimes emulate the external forms of a vegetable 

 to such a degree, that one must be well acquainted with the 

 plants of these families not to be deceived with respect to them. 



• Annals of Philosophy, 1814, voL i. p. 217. 



f Creological Transactions, 1st series, vol. ii. p. 510. 



