STEERE: BRYOLOGY 279 



mosses, some very fundamental ideas have been brought forth by Loeske (1910, 

 1935) with regard to the systematics, phylogeny, and species problem of this 

 group. The most widely accepted classification of Musci at present is that pro- 

 posed by Fleischer (1920, 1904-1924), and established on a still firmer basis by 

 Brotherus (1924-1925). Dixon (in Verdoorn, 1932) gives one of the most re- 

 cent views on the classification of Musci. The concept of genera in Musci and its 

 attendant problems has been discussed by Steere (1947). 



Phylogeny 



The phylogeny of bryophytes has been investigated by several methods, most 

 commonly through studies of the comparative morphology of living forms (Loe- 

 ske, 1910; Schiffner, 1917), through the use of serological tests (Stepputat and 

 Ziegenspeck, 1929), and through the study of fossil forms (Harris, 1939; Bark- 

 man, 1950). Although earlier morphologists proposed that the Bryophyta are 

 derived directly from the Chloro])hyceae, from the Phaeophyceae (Church, 

 1919), or from some common ancestor of the Pteridophyta, the recent discovery 

 of primitive Devonian psilophytes, RJiynia and Ilornea, with more than a su- 

 perficial resemblance to members of the Anthocerotae, suggests that the Bryo- 

 phyta may be reduction forms of some group of primitive pteridophytes (Smith, 

 1938; Haskell, 1949). Zimmerman's excellent review (in Verdoorn, 1932) sum- 

 marizes in concise fashion the ideas on bryological phylogeny. 



Paleobryology 



The large number of bryophytes that have been discovered in fossil condi- 

 tion is surprising, in view of the lack of lignified or of heavily cutinized tissues 

 in these plants. Thallose hepatics of a distinctly modern appearance are well 

 known from Carboniferous deposits in England, and there is some evidence for 

 the existence of mosses during the same epoch (Walton, 1928). Harris (1938, 

 1939) provides excellent accounts of Naiadita, a fossil bryophyte from the Trias- 

 sic of England, in so complete and detailed a fashion that a good deal of liglit 

 is shed on the ancestral forms of present-day bryophytes. Dixon (1927) listed 

 very completely the fossil Musci reported up to that time, and a survey of the 

 Cenozoie and Mesozoic bryophytes of North America has appeared rather re- 

 cently (Steere, 1946b). Most of the bryophytes known in fossil condition are 

 relatively recent, occurring in Pleistocene and post-Pleistocene deposits, so that 

 a great many of them might be termed subfossil. As might be expected, a large 

 proportion of the Quaternary bryophytes still survive at the present time. Be- 

 cause of their excellent state of preservation, these subfossil specimens are easily 

 identified through the use of modern manuals, and consequently are of real 

 value in investigations of geographic distribution of the plants of former times 

 (Gams, in Verdoorn, 1932), as indicators of intergiacial climates (Steere, 1942), 

 and to supplement data gained through pollen studies (Meijer, 1950). This 

 modern and useful aspect of bryology has yet been hardly touched. 



Summary 



The past century has produced substantial progress in the field of bryology, 

 especially in descriptive systematics, floristics, and morphology. The application 



