DESMIB FLORA OF DARTMOOR. 251 



Some two hundred gatherings in all were made over the district 

 described and the method of collecting and preserving the 

 material has been described in a previous communication to the 

 Journal of the Quekett Microscopical Club (5). With 

 regard to those methods I may say that additional experience 

 with them has proved their general usefulness and reliability. 

 Material collected two years ago is still in a perfect state of pre- 

 servation and available for further examination. Dr. Rendle 

 has called attention to the value of copper salts for preserving 

 the colour of chlorophyll (6) and Jorgensen has given an explana- 

 tion of the chemical reactions involved (7). One rather striking 

 feature has been noticed in the stored material. When the 

 killing and fixing agent was first added to the gathering, and for 

 months afterwards, no sign of life appeared, but during the last 

 six or nine months micro-organisms have commenced to appear 

 in increasing numbers although the amount of killing fluid added 

 was sufficient to destroy life in all the aquatic larvae, Entomos- 

 traca, etc., present in the gathering. Richet has said that 

 micro-organisms can acquire immunity towards certain anti- 

 septics, which immunity can be transmitted. This would 

 explain why subsequent additions of the fixing agent have failed 

 to check the increase. 



The material was collected during the months of July, August, 

 September and October in 1915 and 1916. These two years in 

 Devonshire were marked by long spells of dry and bright weather. 

 In 1915 during five weeks' collecting on Dartmoor in August 

 and September rain was experienced only for a few hours on 

 three days, the rest of the time being almost unclouded sun- 

 shine. In 1916 an equally dry and bright period was experienced 

 when collecting around Lydford in August. On this trip a 

 moor-pool under Fur Tor at an altitude of about 1,877 feet was 

 observed to have shrunk to such meagre dimensions that only a 

 few gallons of water remained in the peaty bottom. The great 

 heat experienced about that time had heated this residuum 

 until it was quite tepid, yet abundant aquatic life was living in 

 a congested state in it. Several individuals of Dytiscus mar- 

 ginalis, numerous species of Entomostraca and some sixty 

 species and varieties of desmids were collected from it. It has 



