362 PLANT-LIFE 



it has established conditions suited to their needs. 

 The Bog Bean (Menyanthes trifoliata, Plate LXXIV.), 

 Marsh Marigold (Caltka palustris, Plate VIII.) , Marsh 

 Cinquefoil (Comarum palustre), Bog Pimpernel (Anagallis 

 tenella, Plate XXV.) and Marsh Violet (Viola palustris) 

 have taken hold. The silting-up process still proceeds, 

 and is preparing the way for Queen of the Meadow 

 (Spircea ulmaria, Plate LXVIII.) and other plants which 

 are even now encroaching on the Marsh association. If 

 the development is not arrested, the pond will entirely 

 disappear, and its area be occupied by a Grassland 

 association which will be invaded by Alders (Alnus 

 glutinosa, Fig. 68) and Willows, which are already in 

 close proximity. 



We may speak of " fixed " formations, but the 

 term is relative, not absolute. A formation will remain 

 fixed so long as the ecological factors do not change; 

 when the equilibrium of these factors is disturbed, a 

 formation changes. Man in his determination to con- 

 quer Nature and cultivate her soil is a disturbing factor, 

 and in a country like England, which has been under 

 cultivation for many centuries, there are great areas 

 in which ecological determinations are difficult to arrive 

 at. -Yet on British heaths, moors, and seashores, with 

 their dunes and salt-marshes, we have excellent oppor- 

 tunities for ecological study. 



In the hands of the zealous ecologist the science of 

 botany has a great future. Already the study has 

 given a considerable impetus to field work. It has 

 " caught on " in America and on the Continent, and is 

 developing satisfactorily in Britain. We look forward 

 to the time when an ecological survey of the world's 



