STEERE: BRYOLOGY 275 



remarkable restriction of some species to very specific substrata. Excellent re- 

 views of progress in our understanding of the associations of bryophytes have 

 been given by Gams (in Verdoorn, 1932) and by Gimingham and Robertson 

 (1950). It is encouraging to note the greatly increasing use of bryological data 

 in general studies of plant sociology, primarily in Europe, as for example in 

 those of Braun-Blanquet (1948) and Du Rietz (1949). A brief comparison of 

 the pages of the Joui-nal of Ecology (British) and of Ecology (American) will 

 demonstrate rather conclusively the extensive utilization of bryological data by 

 European ecologists and the serious neglect of such data by American workers, 

 with a few outstanding exceptions. The autoecological aspects of bryology have 

 been studied even more than the sociological ones, although the two approaches 

 are often not too well distinguished by workers. Richards (in Verdoorn, 1932)' 

 has provided an excellent review of the effect of environmental factors on the 

 distribution of bryophytes, and has also compiled a useful list of ecological 

 literature (1940). Examples of some recent ecological papers with emphasis on 

 bryological communities and successions follows : on the bryophytes of bogs and 

 swamps (Sjors, 1948), of aquatic habitats (Sorensen, 1948), of the trunks of 

 living trees (Phillips, 1951), of bare soils (Waldheim, 1947), of the steppes of 

 Hungary (Gams, 1934), on sand (Jalas, 1950), on granite rock (Keever, Costing 

 and Anderson, 1951), on volcanic ash (Griggs, 1935), on the leaves of higher 

 plants (Schiffner, 1929; Vanden Berghen, 1949), on rotting wood and on shaded 

 rocks (Jovet and Jovet, 1944), and of snow-beds (Gjaervoll, 1950). Examples of 

 recent ecological studies emphasizing the effects of different environmental fac- 

 tors with relation to the distribution of bryophytes concern the effect of bark 

 composition (Billings and Drew, 1938), of hydrogen-ion concentration (Meyer 

 and Ford, 1943; Apinis and Diogues, 1933; Apinis and Lacis, 1936; Sorensen, 

 1948), of nitrogen lack (Griggs, 1934), of water depth (Persson, 1944a), of low 

 temperatures (Koppe, 1931; Becquerel, 1949; Morrill, 1950), of evaporation 

 (Potzger, 1939), of brackish water (Luther, 1951), of burning (Doignon, 1949), 

 of mineral soils (Persson, 1948), of drying out (Hofleur, 1942; Buch, 1947a), 

 of trace elements (Biebl, 1947), of wave length of light (Teodoresco, 1929), 

 and of wind (Persson, 1944b). 



Morphology 



The distinctive morphology of bryophytes early attracted much attention 

 which resulted in several discoveries important in developing general botanical 

 principles. Although the life history of bryophytes was known in a superficial 

 way from the beginning of the nineteenth century, the regular alternation of 

 sexual and asexual generations was not clearly demonstrated until the exact 

 beginning of the very century under consideration (Hofmeister, 1851). The con- 

 comitant cytological significance of an alternation of a diploid, spore-producing 

 generation with a haploid, gamete-producing generation was not recognized un- 

 til considerably later, however; apparently by Strasburger (1894). These two 

 great discoveries set into motion a long series of serious and detailed investiga- 

 tions, by means of which we now know much about the behavior and structure 

 of many groups of bryophytes. The impressive works of Leitgeb (1874-1881), 

 Bower (1935), Campbell (1940), and Goebel (1930-1933) not only summarize 



