350 SECTIONAL TRANSACTIONS.— C. 



With favourable specimens the pyrites may be completely removed. In order to 

 obtain successful results the greatest care must be exercised in the final poUahing of the 

 section. 



Dr. E. Neaverson. 



Methods of preparing fossil brachiopods to show internal features depend upon 

 the preservation of the fossil, the nature of its matrix, and on the features which it is 

 desired to exhibits— whether brachial supports projecting freely into the shell cavity, 

 or muscle-scars and ovarian markings impressed upon the internal surface of the shell. 

 Various methods of preparation will be discussed and illustrated. 



Dr. H. Hamshaw Thomas. — The Investigation of the Structure of 

 Mummified Fossil Plants. « 



The old method of maceration which reveals the structure of cutinised ceUs can be 

 used for some bulky remains, such as buds or fruits, and the membranes and remains 

 of spores, which can often be extracted from them, show that some of the internal 

 structure is preserved. A method has been devised for investigating the structure of 

 the fruits of Caytonia, which at first seemed composed of homogeneous material. 



The fruits are removed from the rock, cleaned, softened, embedded in ceUoidin and 

 cut into thin sections with a microtome. The sections, which show little or no structure, 

 are now treated with reagents, which effect a partial solution of the material, and in so 

 doing render the structure visible. Good results were obtained with KCIO3 in strong 

 HCl, followed by a very dilute alkaUne solution. The sections were subsequently 

 stained and mounted. By this treatment, cutinised, stony, or fibrous tissues become 

 visible. Other solvents reveal the position of the middle lamella of the ceU walls. 

 The method is probably capable of extension to some other plant remains, but possesses 

 certain difficulties. 



jVIr. JoHK Walton. — The Transfer Method of Examining Fossil 

 Plant ' Impressions' ' 



The surface of an ordinary hand-specimen of an ' impression,' or what is more 

 correctly termed ' incrustation,' of a fossil plant is usually a damaged surface ; this 

 is a necessary consequence of the fact that in order to expose such a fossil to view the 

 rock must be split open. The two surfaces of a plant-fragment are usually of a different 

 nature, and the split tends to pass over and expose to view the more even of the two 

 surfaces. The other surface is not shown ; it is probably the most interesting, and, 

 as it may bear sporangia, hairs, or other emergences, it is an advantage to be able 

 to expose it to view in an undamaged condition. 



This may be done by cementing the specimen face down to a glass slide with fused 

 Canada balsam, protecting the uncovered glass surface with wax. By removing 

 the rock with hydrofluoric or some other suitable acid, the plant residue is left sticking 

 to the balsam, and the surface of the plant originally hidden next the rock is now 

 exposed to view. 



As the support and cement are transparent, the fossil may now be examined by 

 transmitted light, and many such fossils will reveal a certain amount of structure 

 when seen in this way. When the fossil to be examined consists of very fragile films 

 or particles of organic material, the method of transfer enables one to examine them 

 by transmitted light without any alteration in their space relationship to one another. 

 In many instances a fossil of a leaf may be represented by numerous particles ; the 

 fossil, if removed from the rock by direct maceration, is resolved into its particles, 

 which separately may exhibit no structure, but if kept together in a transfer often 

 reveal otherwise unobservable features. 



A great improvement on this method, more particularly in its application to the 

 examination of small organic particles and thin organic films, has been devised by 

 Mr. E. Ashby (to be described shortly by Prof. W. H. Lang in the Annals of Botany). 

 This consists in using a cellulose film instead of balsam as a support for the fossil 

 residues. The main advantage gained by this device is the possibility of making 

 preparations of a more permanent nature and in avoiding the use of glass slides and 

 paraffin-wax. It is not, however, of such general application as the balsam method, 



1 Described in the Annals of Botany, vol. xxxvii., July 1923. 



