exhibit all the different tones of colour, from the most brilliant grass green to the darkest sap or lightest yellow green which at present characterize the different living specimens with which we are acquainted. At times however the fibre assumes a whitish aspect, or the yellowish and reddish hue which those delicate plants exhibit when dead, an appearance perhaps even more characteristic of their vegetable nature than their natural colour, since we cannot easily understand how it could be imitated either by chlorite or by metallic oxides.
Botanists who are conversant with the difficulty of ascertaining the species of most of the plants contained in the troublesome class of Cryptogamia, and the uncertainty in particular, which, notwithstanding the meritorious labours of many modern authors, still hangs over the individuals of the genus Conferva, will not be surprized that I have made no attempt to ascertain the species occurring in chalcedonies. They well know the obscurity which attends this pursuit, even where access to numerous examples of the living plant, with the power of turning it in every direction, of viewing it in all its states of growth, and of dissecting it into all its ramifications, facilitate the investigation. With regard to the greater number of species indeed, it is known that no distinction can be traced, nor any accurate character laid down, even by moderate magnifying powers. It is only from those highly magnified views of the living specimen which are capable of exhibiting the peculiarities of its internal structure, and the disposition of its fructification, that characters can be formed or individuals distinguished. This sort of investigation cannot be applied to the remains in question, as the loss of light which necessarily follows the attempt to apply high powers, added to the great diminution of it when transmitted through the chalcedony, entirely deprives us of a sight of them. But in the paper of Daubenton,