American Species of Marchantia. 223 



genera. Sprtice-^^ mentions the occasional presence of three 

 furrows in the stalk of tlie female receptacle in Marchantia, with- 

 out citing definite species ; Leitgeb,^" in a single instance, found 

 four furrows in the stalk of the female receptacle in Preissia 

 quadrata; Stephani^^ states that the stalk of the male receptacle 

 in the African M. Wilmsii Steph. has four furrows but doubts 

 the constancy of this condition; and Schiffner*- notes that the 

 stalk of the female receptacle in Bucegia romanica Radian some- 

 times shows four furrows. These seem to be the only references 

 to more than two furrows in the literature, but in all probability 

 a higher number than two would occasionally be found in most 

 species of MarcJiantia if enough stalks were examined. In M. 

 breviloba four furrows seem to be the rule in the female recep- 

 tacle, although it would hardly be safe to state that four were 

 always present. 



In the case of j\f. polymorpha it was noted long ago by Mirbel 

 that the dorsal side of the stalk of the female receptacle showed 

 a distinct strip of photosynthetic tissue with air-chambers, epi- 

 dermal pores and short green filaments. This strip seems to be 

 of constant occurrence throughout the genus. It commences 

 close to the base of the stalk and extends nearly to the disc. In 

 most cases the strip is continuous (Figs. 5, K; 8, J; 9, K; 

 etc.) but sometimes, as in M. cJicnopoda, it may be separated into 

 two strips by a median groove (Fig. 20, G-I). In the stalk of 

 the male receptacle photosynthetic tissue is usually absent, the 

 dorsal portion being composed of compact parenchyma. In cer- 

 tain species, however, such as il/. domingensis, the photosynthetic 

 tissue is about as well developed in the male (Fig. 12, A) as in 

 the female receptacle. In M. breviloba the lower part (Fig. 

 9, I) of the stalk develops photosynthetic tissue while the upper 

 part (Fig. 9, J) lacks it completely. 



In the disc of the male receptacle the dichotomous branching 

 usually continues and a distinct division into rays becomes 

 apparent. x\lthough the number of rays is subject to variation, 

 certain numbers seem to be normal or typical for certain species. 

 In M. polymorpha, for example, there are usually eight rays 



^ Trans. Bot. Soc. Edinburgh 15 : 558. 1885. 



**Unters. iiber Leberm. 6:31. 1881. 



*^ Hedwigia 31 : 196. 1892. 



*" Beih. Bot. Centralbl. 23= : 282. /. 16. 1908. 



