STABLE AND MIGRATORY PLANT FORMATIONS 1 33 



association of species which individually grow in other 

 habitats. Spring associations appear to be clearly demar- 

 cated by the extent of the focus within which the waters 

 retain certain definite characters, but where the waters have a 

 fairly large and constant volume certain species may follow 

 the watercourses for considerable distances. Spring plant 

 associations are most evident in the mountainous districts of 

 this country, since the original relations of the drainage and 

 vegetation have usually there been less interfered with. 

 High level springs with Philonotis, Epilobmm alpinuni, 

 Saxifraga stellaris (3) (p. 326), etc., can be distinguished 

 from springs in the moorland bogs with Hypnuvi revolvens, 

 Sphagmcin, Stellaria uliginosa, etc., and these again from 

 springs arising on the lower alluvial terraces with Hypnuin 

 cuspidatuni and others ; but various stages can often be 

 recognised leading from one to the other, w^hile some show 

 peculiarities of their own demonstrating that the plants are 

 highly susceptible to conditions which vary at different 

 springs, and which, as yet, have received practically no 

 attention b}' plant ecologists. Groups of species, including 

 one or another of the above, or of the following (yDicranella 

 squarrosa, Hypmun sarnientosuin, Hypnum strainineuin^ 

 Hypnuin scorpioides, Hypmon coinniiitatum ^ Amblystegmin 

 filicinuin, Mnhun punctatinn, Bryuni alpinum, B. pallens^ 

 B. Diivalii, Webera albicans^ and species of Aneura, Scap- 

 ania, KndSphagnujn, Selaginella,Montia, Ranuncuhis,Myosotis, 

 Ckrysospleniinn^ and others), are commonly met with in our 

 moorland districts again and again in precisely similar 

 surroundings, which are often difficult to define and need 

 careful examination. In other words, the fact that the 

 plants are aquatic or semi-aquatic, and that the water is 

 flowing, will not define a spring association, but rather the 

 tout ensemble of conditions as included in the physiography, 

 not only in its direct physical influence, but also in its 

 influence on the country's fauna, whether this be as a home, 

 death trap, barrier, or an invitation to drink. There is often 

 a striking physiognomy in the floating carpet associations 

 of gentle but constant springs, the mosses, hepatics, and 

 phanerogams alike assuming a close-pressed, fastigiate 

 growth, that is presumably to be explained as the result of 



