THE BOG-MOSSES OF ESSEX. 113 



In addition to these lists there are specimens of bog-mosses 

 collected in Essex, in the following Herbaria : — 



(9) British Museum of Natural History. 

 (10) Essex Field Club Herbarium. 



(Including the collections of Messrs. English and Varenne.) 

 All of these sources of information have been consulted in 

 drawing up the list, and the records duly incorporated. 



The Sphagnaceae so far as their vegetative structure is 

 concerned, form a highly specialized group, and are particularly 

 well adapted for life in situations where there is an abundant 

 and constant supply of water contained in shallow basins and 

 flowing but slowly, if at all. The majority of the species appear 

 to thrive best in the presence of abundant light. These some- 

 what peculiar conditions are realised in few places in our count)', 

 and only, it would seem, where a porous stratum forming the 

 top of a hill meets a non-porous stratum as one goes down the 

 slope. Except where drainage, either for agricultural purposes 

 or for building, has altered the conditions, they are fulfilled 

 wherever the Bagshot Sands overlie the Boulder Clay or the 

 London Clay, and in some places where Glacial Gravel forms 

 the crown of the hill, the lower portion of which is of Boulder 

 Clay or London Clay. 



I have collected Sphagna in the following localities where 

 London Clay underlies Bagshot Sands — Warley, Norton Heath, 

 High Beach, Galleywood Common, Mill Green, and Hainhault 

 Forest. In all the other localities where I have found these 

 plants growing, the drift maps show Glacial Gravel (Post-glacial 

 at the Rising Sun, Walthamstow), except at the locality in 

 Thomas' Quarters, Epping Forest, and there the map must be 

 at fault. I have not found any Sphagna definitely associated 

 with the Boulder Clay that forms so large a part of the surface 

 of the County — possibly owing to the presence of a fairly large 

 proportion of lime in that formation. 



[Note. — In the following list the names in brackets refer to the collector of 

 the specimen quoted. I have examined those from localities followed 

 by the sign ! and have collected a specimen in the localities followed 

 by! !] 



