7D4 MR FRANCIS J. LEWIS 



Technique. — Very little can be made out from the peat in the condition in which it 

 is collected from the various sections. It is easy to recognise certain characteristic 

 plants such as Calluna, Scirpus, Carex, Eriophorum, Empetrum, Salix ; but for the 

 proper collection of seeds, fruits, and leaves, and the smaller plant remains — such as 

 mosses, algae, diatoms, pollen grains, of which so much of the peat is built up — it is 

 necessary to treat the material by detailed analysis in the laboratory. 



During the examination of material described in this paper, I have used the carbonate- 

 soda method described by Mrs E. M. Reid (l), and the nitric-acid method described 

 by Gcnnar Andersson (2). The first method consists of boiling the peat in a con- 

 centrated solution of carbonate of soda until the various humous acids cementing the 

 plant remains together are completely dissolved. In the other method the peat is 

 placed in dilute nitric acid until it is completely oxidised, when the material becomes 

 filled with bubbles of gas and the plant remains fall apart. The former method gives 

 satisfactory results, particularly with extremely hard, dry peat, but the nitric acid 

 possesses certain advantages over the carbonate of soda ; with the former method the 

 peat is bleached, and it becomes easier to separate the seeds from the rest of the 

 material, and this is further facilitated by the gas contained in the seeds, which causes 

 them to float on the surface of the water. The best results are obtained by immersing 

 the peat in from 10 per cent, to 50 per cent, nitric acid, according to the amount of 

 water contained in the peat and the closeness of texture of the material. Prolonged 

 treatment with weak solutions is more satisfactory than rapid treatment with strong 

 acid. After the material has been thoroughly separated by the action of the acid, it is 

 poured into a metal or glass cone fitted with several sieves of varying mesh, and is 

 washed by a continuous stream of water. In the collection of the finer material, such 

 as pollen grains, algse, diatoms, the wash is collected in tubes as it issues from the outlet 

 at the base of the cone. The coarser material quickly settles to the bottom, and 

 samples can be collected with a pipette and mounted in glycerine or Ferrant's solution 

 for examination under the microscope. The finer material which remains in suspension 

 can be collected by placing a small quantity of the water in a centrifuge. The most 

 delicate organisms, such as diatoms, desmids, and pollen grains, can be collected in this 

 manner and are frequently quite uninjured. 



The larger fossils which remain in the sieves after washing are placed in glass dishes 

 and separated from the shreds of epidermis, rootlets, etc., under a dissecting microscope. 



Serial sections, with a Cambridge rocker microtome, can be made from small squares 

 of peat by the usual method and mounted in Canada balsam, but no staining is required, 

 owing to the natural dark brown colour of the peat. 



During the last seven years thirty-seven districts in Scotland and one in England 

 have been examined, and every quarter of Scotland in which peat deposits occur has 

 been laid under contribution, except west of a line drawn from Oban through Glasgow 

 to Ayr. These districts have been fully described in former papers, and a brief summary 

 of the salient features is given in Part III. of this series (3). 



