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THE AMERICAN NATURALIST [Vol. XLVI 



they range from almost microscopic forms like some of the 

 minute epiphyllous Lejeuniaceae, to stout species like some of the 

 tropical Frullanias, which form pendant masses several feet in 



In all the Acrogynse the archegonia are in groups terminating 

 the fertile branch, whose further growth is arrested by the trans- 

 formation of the apical cell into an archegonium. 



The sporogonium is always well developed, usually showing a 

 well-marked foot and seta. Perfect elaters are always present. 

 A small number only of the Acrogynae have been studied crit- 

 ically with reference to the development of the sporophyte, and 

 much more work must be done before the real affinities of some 

 of the genera can be determined satisfactorily. 



On the basis of our present knowledge of the group, Cavers 

 proposes a classification based largely upon the work of Spruce. 

 He recognizes two main divisions, the first including a single 

 very large family, Lejeuniaceae, with nearly 2,000 species; the 

 second contains seven families, of which three, viz., Porellaceae, 

 Pleuroziaceae and Radulaceas, are regarded as natural families, 

 the other four as more or less artificial, the limits between them 

 being difficult to define. 



The inter-relationships of the Acrogynae are extremely difficult 

 to follow. A number of students of the liverworts, notably 

 Spruce and Schiffner, believe that the group is of polyphyletic 

 origin, the Lejeuniaceae representing a quite distinct line derived 

 from forms allied to the Aneuraceae. There are striking resem- 

 blances both of gametophyte and sporophyte, the former in some 

 cases having a protonemal stage of long duration, and very much 

 resembling one of the simpler thallose liverworts. Cavers be- 

 lieves, however, that these resemblances are simply parallel devel- 

 opments, and not true homologies; and, as already stated, that 

 the Acrogynae represent a single line of development. Of these 

 forms he states that Lophozia probably comes nearer to the as- 

 sumed ancestral type. 



From the Lophozia type, three branches are traced, one 

 through Plagiochila developing a large number of genera, among 

 which Ccphalozia, again, is the starting-point for the develop- 

 ment of a number of specialized genera like Zoopsis, Lepidozia, 

 and Tnchocolea. The second line leads through Marsupiella 

 and \«nha to a number of genera, of which the highest are 

 Stephaniella, Gyrothyra and Symphyomitra. The third line, 



