American Species of Marchantia. 2^1 



4. Rhizoids 



The rhizoids in the genus Marchantia, as in practically all of 

 the Marchantiales, are of two types, the smooth and the tuber- 

 culate. In the smooth type the walls are thin or uniformly 

 thickened; in the tuberculate type numerous local thickenings 

 of the wall extend into the lumen of the rhizoid in the form of 

 cylindrical or bluntly conical projections. In some of the tuber- 

 culate rhizoids the projections are discrete and irregular in their 

 distribution; in others they are more or less coalescent and show 

 a spiral arrangement. Kamerling^^ has shown that these spiral 

 tuberculate rhizoids are abundant in M. polymorpha and Schiff- 

 ner^^ has examined this and other species of the genus with 

 reference to these peculiar structures. He confirms Kamerling's 

 I statements about their occurrence in M. polymorpha and finds, 

 so far as American species are concerned, that they are equally 

 I abundant and typical in M. chenopoda; that they still occur, 

 I although in less typical form, in M. domingensis and its allies; 

 and they are wanting altogether in M. paleacea. 



Most of the rhizoids in Marchantia run in parallel bundles 

 under the scales and converge to form a single large median 

 bundle. There are, however, numerous rhizoids in the thickened 

 median portion which spread at right angles to the surface, and 

 Schiffner has made a number of interesting observations on these. 

 In forms of M. polymorpha where a definite dorsal band lacks 

 air-chambers, the rhizoids in question are smooth; in forms 

 where the air-chambers extend across the median region, the 

 rhizoids are tuberculate. In M. plicata the spreading rhizoids 

 are smooth; in M. chenopoda, smooth; in M. Berteroana, 

 tuberculate ; in M. paleacea, smooth or with scattered tubercles. 

 These differences may sometimes be of help in distinguishing 

 species. 



5. Receptacles 



The receptacles in Marchantia are strikingly different from the 

 vegetative branches and attain a higher degree of complexity than 

 in any other genus of the group. Two distinct portions may be 

 distinguished, the erect stalk and the horizontal disc (or recep- 



" Flora 84 (Erganzungsb.) : 31- pl- ^> 2, /. 7- 1897. 



^Ann. Jard. Bot. Buitenzorg 2 (Suppl. 3) 1489, 490. 1909. 



