516 Dr. Mac Culloch on Vegetable remains 



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 ex- 

 hibit 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, notwith- 

 standing 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 chal- 

 cedonies. 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 in- 

 deed, it is known that no distinction can be traced, nor any accurate 

 character laid down, even by moderate magnifying powers. It i& 

 only from those highly magnified views of the living specimen 

 which are capable of exhibiting the peculiarities of its internal struc- 

 ture, and the disposition of its fructification, that characters can be 

 formed or individuals distinguished. This sort of investigation can- 

 not 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, en- 

 tirely deprives us of a sight of them. But in the paper of Daubenton, 



