THE AMERICAN NATURALIST 



[Vol. XLVI 



species of delicate liverworts inhabiting dark crevices in rocks, 

 or shallow caves. All the species show evidences of marked 

 structural modifications due to their unusual habitat. C. fceti- 

 dissimum is a characteristic species of the Indo-Malayan region. 



The simple genus Monoclea with two species represents very 

 distinct the family Monocleaceae. In his great work on the Hepat- 

 icas, Leitgeb referred Monoclea to the Jungermanniales, and this 

 view was adopted by Schiffner in his treatment of the Hepaticoe 

 in Engler & Prantl's "Natiirliche Pflanzenfamilien. " This asso- 

 ciation with the Jungermanniales was mainly on account of the 

 structure of the thallus, which is quite destitute of the air- 

 chambers which distinguish most of the Marchantiales. There is 

 also in Monoclea no definite archegonial receptacle, and the soli- 

 tary sporogonium has a long seta like that of many Jungerman- 

 niales. 



All the more recent students of Monoclea, however, are agreed 

 that the plant really belongs to the Marchantiales, this being 

 shown both by the structure of the thallus, and that of the repro- 

 ductive organs. The absence of air-chambers is with little ques- 

 tion to be looked upon as a secondary condition, due to the semi- 

 aquatic habit of the plant. A similar disappearance of the air- 

 chambers is known in the unmistakable marchantiaceous genus 

 Dumortiera. 



Leitgeb, in his important memoirs on the Hepatica?, recognized 

 three types of archegonial receptacle. Only in one of these was 

 the receptacle compound in its structure. More recent studies, 

 including those of Cavers, indicate that this compound or "com- 

 posite" type is much more general than Leitgeb supposed. 

 Cavers states that probably all of the genera of the Marchan- 

 tiaceaa, except Clevea and Plagiochasma, will be found to have 

 receptacles of the composite type. 



In tracing the phylogeny of the Marchantiales, Cavers distin- 

 guishes two main divergent groups which are connected with the 

 Kicciaceffi by Corsinia and Boschia, respectively. The first series 

 includes, among other genera, Clevea, Plagiochasma, Reooulia 

 imd Ftmbriaria, the latter representing the culmination of this 

 series. 



The second series, starting with Boschia, shows two main 

 branches, one including the Targioniace* and Monoclea, the 

 other the most highly developed genera, like Fegatella, Dumor- 



