270 M. Brongniart's Observations on the Arborizations in 



Anxious, therefore, to assure myself of the nature of these al- 

 leged vegetables, I examined a considerable number of moss 

 agates, belonging either to public collections or to those of pri- 

 vate individuals in Paris. I observed them not with a simple 

 lens, but with Amici's excellent microscope; of which, however, 

 I only employed the low magnifying powers of from 50 to about 

 100 diameters. In more cases, the transparency of these agates 

 enabled me to see distinctly, at least in certain points, the dis- 

 position of the filaments, and I was enabled to assure myself, 

 not only that they had none of the characters of plants of the 

 family of Confervae, or of any other plant, but that they even 

 presented characters which proved them to be mere infiltrations, 

 and not vegetables. I have represented, in figs. 7 and 8 of 

 Plate I. of my work on Fossil Plants, the two forms under 

 which these infiltrations most commonly presented themselves. 

 Fig. 7 shews the disposition which the brown infiltrations of the 

 nearly opaque moss agates generally adopt. The filaments, 

 which are very irregular as to their size and mode of division, 

 are variously bulged. They are pretty distinctly defined, with- 

 out any nebulosity around them, and appear formed by knotty 

 matter, of a dark-brown colour, filling numerous filiform and 

 irregular canals, distributed without order in the calcedony. 

 These infiltrations are very often irregularly anastomosed, which 

 precludes all idea of a confervoid plant, since in the only cases in 

 which similar anastomoses exist among the conferva?, they 

 give rise to a very irregular net-work, as in the Hydrodyction, 

 or to a mode of reticulation, irregular it is true, but very dis- 

 tinct from that of these infiltrations, and such as is observed in 

 the conjugata, particularly in the Zyg7iema genitfleanmi. The 

 only plants I know, whose irregular anastomoses resemble, in 

 some respects, those presented by the infiltration in question, are 

 in the genus Rhizomorpha, a genus which, in no other respect, 

 has any resemblance to the infiltration of agates. 



These brown infiltrations are the most frequent, but the most 

 remarkable, on account of their agreeable appearance, and their 

 resemblance, at first sight, to confervae, are the green infiltra- 

 tions. The matter, which forms them, appears much thinner 

 than that of the brown infiltrations, so that it has, as it were, 

 tinged the calcedony to some distance from the small canals in 



