REGRESSION. 151 



formation as the chief associations, an incomplete or imbalanced picture of the 

 vegetation results." 



In the first paragraph the real identity of retrogression with destruction and 

 denudation is clearly indicated by the author in the statements that the stable 

 association of Glyceria maritima may be destroyed by the waves, and that 

 retrogressive associations are recognizable in denuding peat-moss. More- 

 over, he ignores the part light plays in determining habitat Umits, and 

 consequently the normal developmental relation of reaction to changes of 

 population. The production of new areas by denudation and by deposition 

 is distinctly pointed out, but the essential correlation of this with succession is 

 not made (plate 45 a). 



The views of Moss were adopted by Tansley and several of his associates. 

 Moss, Rankin, and Lewis, in "Types of British Vegetation" (1911): 



"The different types of plant community on the same soil, namely, 'scrub' 

 or bushland, and a corresponding grassland, or heathland, have no doubt 

 originated mainly from the clearing of the woodland, and the pasturing of 

 sheep and cattle. This prevents the generation of the woodland, and of most 

 of the shrubs also, if the pasturage is suflBciently h^ivy and continuous, while 

 it encourages the growth of grasses. Thus the plant formation determined by 

 the particular soil, and once represented by woodland, shows a series of phases 

 of degeneration or retrogression from the original woodland, brought about 

 by the activity of man. The intimate relationship of the various phases is 

 clearly seen in the associated plants. The woodland proper has of course a 

 ground vegetation consisting of charactersitic shade pkuits, but the open 

 places, and the 'drives' and 'rides' of the woods, are occupied by many of the 

 species found among the scrub and in the grassland, while those true woodknd 

 plants, which can endure exposure to bright light and the drier air outside the 

 shelter of the trees, often persist among the grasses of the open. In some cases 

 where grassland is not pastured, the shrubs and trees of the formation recol- 

 onize the open land, and woodland is regenerated. Besides these degenera- 

 tive processes, due to human interference, there are others due to 'natural' 

 causes, which are for the most part little understood." (17) 



The degeneration of Quercetum robwris into subordinate or retrogressive 

 associations of scrub and grassland is described (page 83), and the similar 

 behavior of Quercetum sessiliflorae is discussed (page 130). An instructive 

 discussion of reproduction in beechwood (168) lays bare the successional 

 relations of the beech and ash, and at the same time serves to emphasize the 

 fact that so-called degeneration is not a developmental but a destructive proc- 

 ess due to man and animals. The last statement is also true of the behavior 

 of heather moors, in connection with their repeated destruction by burning 

 every few years (277) (plate 45 b). 



The degeneration (retrogression) of moorland (280) obviously consists of 

 two processes: "The earlier stages of the degeneration of a cotton-grass moor 

 in which the wetter EriopJwretum vaginati is replaced by the drier Vaccinietum 

 myrtilli owing to gradual desiccation of the peat by improved drainage," are 

 merely a normal stage of progressive development in which a hydrophytic 

 sedge is replaced by a more mesophytic shrub. The sequence of life-forms and 

 the reaction upon the water-content both prove that the movement is pro- 

 gressive and truly developmental, the drying due to erosion merely hastening 

 the normal reaction. This is further proved by the statement that : 



