302 A CENTURY OF PROGRESS IN THE NATURAL SCIENCES 



literature further back), one must expect that our present scheme, though un- 

 doubtedly truer than that of a century ago, may still perhaps not be final. 



Modern work on the Pteridophyta may be considered to begin with the 

 publication in 1851 of Hofmeister's Vergleichende Untersiichungen. This book, 

 better known to some readers as The Higher Cryptogmnia in the later English 

 edition of 1862, is a landmark in the history of botany and probably the most 

 important botanical product of either year. It is the first, and still in many ways 

 the most detailed and informative, general account of the life histories and re- 

 productive structures of the main types of Bryophyta and Pteridophyta to- 

 gether with some, though less complete, reference to the gymnosperms. Within 

 the Pteridophyta there are descriptions of prothalli, sex organs, and develop- 

 mental stages in numerous ferns, including PiluJaria, Marsilea, Salvinia, Botry- 

 chium, and OphiogJossum (though this only at second hand, quoting Mettenius) 

 as well as Equisetum, SelagineUa, and Isoetes. At one stroke the facts of alter- 

 nation of generations are spread before one almost in their entirety, and indeed 

 we only need to quote the subsequent addition of the nuclear cycle to the story 

 ( Strasburger, 1894) and the discovery of apogamy (Farlow, 1874; De Bary, 

 1878) and apospory (Druery and Bower, 1884; Bower, 1887) to have substan- 

 tially our present knowledge of the basic facts of the pteridophytic life cycle. 

 Induced apogamy as a facultative process resulting from prevention of fertiliza- 

 tion in a normal sexual species was detected by Heim (1896) and further eluci- 

 dated by Lang in 1898. Induced apospory, as opposed to the genetically deter- 

 mined sort, was produced on detached fern leaves by Goebel (1908) and, by 

 another method on young leaves in situ, by Lang (1924). To these observa- 

 tions and experiments the cytological facts, and in particular those of the poly- 

 ploid series, have subsequently been added (cf. Lawton, 1932; Manton, 1932; 

 Dopp, 1932; Duncan, 1941; and Manton, 1950). Morphological and experi- 

 mental observations have been extended to other species (for further literature 

 see Campbell, 1918, and Verdoorn, 1938) and a recent renewed interest in fern 

 prothalli is contributing gametophytic characters to discussions of phyletic de- 

 tails (cf. Stokey, 1951). In a first reading of Ilofmeister, however, the absence 

 of these later developments is unimportant. It requires an effort of mind to 

 realize that the date of the Vergleichende Untersuchungen is pre-Darwinian and 

 that the logical coherence which it introduces into the taxonomy of the major 

 groups of land plants is not a result of evolutionary thinking but is one of 

 the most spectacular achievements of the comparative morphological study of 

 development. 



Speculative thinking 'round the facts of alternation of generations followed 

 later and need not be discussed in detail here since much of it will doubtless 

 have been recorded in connection with other groups of plants, such as the Bryo- 

 phyta, to which it is equally relevant. An excellent short summary of the period 

 starting with Celakovsky (1874) to the publication of The Origin of a Land 

 Flora by Bower in 1908 is given by Bower (1935, pp. 484-491). Both these last 

 publications are important for the clear exposition of the view that "the Arche- 

 goniate sporophyte, or diplophase, is a stage interpolated in the course of evo- 

 lution between the successive events of syngamy and meiosis; and that the 

 neutral somatic development is not strictly homogenetic with the sexual. ..." 

 (Bower, 1935, p. 491.) This idea of the gradual interpolation of a new phase 



