276 A CENTURY OF PROGRESS IN THE NATURAL SCIENCES 



the status of bryological morphology of the time, but also include much new ma- 

 terial resulting from original research. Smith's modern reference book (1938) 

 brings together in an exemplary fashion most of the literature of this field. 



Experimental Morphology 



The discovery of anomalous behavior in the life cycle of bryophytes gave 

 an opening for experimental investigations which, in turn, led to a greater un- 

 derstanding of alternation of generations, or at least of the problems involved. 

 Pringsheim (1878) noted that under certain circumstances the seta of a moss 

 sporophyte would produce, through local regeneration, a filamentous protonema, 

 ordinarily considered to be a gametophytic structure. Furthermore, the pro- 

 tonema so originated continues its development in a perfectly normal manner 

 and eventually produces the characteristic green leafy gametophyte plants. 

 Considerably later, the cytological significance of apospory was realized, and 

 stimulated further researches such as those of the Marchals (1911), who were 

 able to produce polyploidy under controlled conditions for the first time. The 

 cytological and genetical implications of tliese brilliant experiments were ob- 

 vious, and led to the extensive researches of Wettstein (1942; in Verdoorn, 

 1932), whose work on the genetics of mosses, in connection with regeneration, 

 apospory, and hybridization between species and genera, is now classic. Some 

 study of apospory in Hepaticae has also been made (Rink, 1935). Springer 

 (1935) reported the bypassing of fertilization, or apogamy, through the direct 

 budding off of a sporophytic structure from gametophytic tissue in a moss, as 

 the result of experiments that have not yet been repeated. Investigation of the 

 ability of bryophytes to reproduce asexually through various vegetative means, 

 as gemmae, brood-bodies, etc., has led to an extensive literature (Degenkolbe, 

 1937; Correns, 1899; Sainsbury, 1952). Because of their sensitive responses to 

 small variations in environment bryophytes furnish good materials for experi- 

 mental research, but are not yet sufficiently appreciated, in spite of some excel- 

 lent work on them (Buch, in Verdoorn, 1932). Research on bryophytes utiliz- 

 ing the techniques of experimental morphology have yielded results of im- 

 portance to plant physiology (Buch, 1947b; La Rue, 1942; Biebl, 1947), to 

 genetics (Wettstein, 1942), to ecology (Dombrowski, 1933; Romose, 1940), and 

 to systematic bryology (Wettstein and Straub, 1942; Arnaudow, 1938). Ernst- 

 Schwarzenbach (1944) demonstrated experimentally the relationship between 

 spore dimorphism and sexuality in mosses. 



Anatomy 



Although the more detailed structural aspects of descriptive morphology are 

 placed under the heading of anatomj^ by many authors, the two fields are ex- 

 ceedingly difficult to distinguish. Nevertheless, unusually complete treatises and 

 summaries have been published on the anatomy of Hepaticae by Herzog (1925), 

 Buch (in Verdoorn, 1932), and K. Miiller (1951), and of Musci by Lorch (1931) 

 and van der Wijk (in Verdoorn, 1932). 



Physiology 



Bryological materials have been used relatively rarely in physiological ex- 

 periments, and the only comprehensive review concerned with the physiology 



