American Species of Marchantia. 221 



4. Rhizoids 



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

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

 ciilate. 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 

 statements about their occurrence in M. polymorpha and finds, 

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

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

 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. pi. i, 2, f. 7. 1897. 



^'Ann. Jard. Bot. Buitenzorg 2 (Suppl. 3) : 489, 490. 1909. 



