12 PAL^ONTOLOGICAL BOTANY. 



ducts have transverse diaphragms. There are numerous 

 medullary rays. The wood in their stems is converted into 

 chalcedony. (Carruthers on Petrified Forest near Cairo. 

 Geol. Mag., July 1870.) 



Examination of the Structure of Fossil Plants. 



When the structure of fossil plants is well preserved, it 

 may be seen under the microscope by making thin sections 

 after the mode recommended by Mr. William Nicol, the 

 inventor of the prism which bears his name, and to whose 

 memory Unger dedicated the genus Nicolia, which has just 

 been described as constituting the petrified forest at Cairo. 

 The following is a description of the process of preparing 

 fossils for the microscope, by Mr. Alexander Bryson. (Edin. 

 N. Phil. Journal, N. S. iii. 297. Balfour's Botanist's Com- 

 panion, p. 30.) 



^' The usual mode of proceeding in making a section of 

 fossil wood is simple, though tedious. The first process is 

 to flatten the specimen to be operated on by grinding it on a 

 flat lap made of lead charged with emery or corundum 

 powder. It must now be rendered perfectly flat by hand on 

 a plate of metal or glass, using much finer emery than in the 

 first operation of grinding. The next operation is to cement 

 the object to the glass plate. Both the plate of glass and 

 the fossil to be cemented must be heated to a temperature 

 rather inconvenient for the fingers to bear. By this means 

 moisture and adherent air are driven off", especially from the 

 object to be operated on. Canada balsam is now to be 

 equally spread over both plate and object, and exposed again 

 to heat, until the redundant turpentine in the balsam has 

 been driven off" by evaporation. The two surfaces are now to 

 be connected while hot, and a slow circular motion, with 

 pressure, given either to the plate or object, for the purpose 

 of throwing out the superabundant balsam and globules of 



