112 H0FME1STER, ON 



preponderating development in thickness and length, and 

 the proportionally small development in breadth, of the 

 median component of the last vegetative shoot. In its 

 earliest youth it exhibits a hemispherical, and at a some- 

 what later period a cylindrical, mass of fleshy, cellular 

 tissue, with a bluntly rounded apex (PL XVI, fig. 5 ; 

 PL XI, fig. 10). Its longitudinal growth results, as is 

 the case in vegetative shoots, from repeated division of the 

 apical cell by means of alternately inclined septa, except 

 that at the first commencement of the formation of the in- 

 florescence no more than one apical cell is present (PL XVI, 

 fig. 5). During the further development there is formed 

 on its under side a deep channel, which is (PL XVI, 

 fig. 7) destined to receive the rootlets which are produced 

 at a later period by the upper pileate portion, into which 

 the apex of the young rudiment of the head of the fruit is 

 transformed by means of active growth in the direction of 

 its breadth. The under side of the stem of some species 

 (Marchantia polymorpha, PL XVI, fig. 17, for instance) 

 exhibits two such channels. In both cases the channels 

 appear to originate in an active multiplication of the cells of 

 the inverted sides of the stem of the receptacle. The root- 

 lets first appear from the lower end of the channel, and pene- 

 trate into the ground. 



The shoot which produces the inflorescence bears nu- 

 merous narrow, scattered leaves, in which the apex always 

 consists of one cell and the base of (at the most) a few 

 cells. The leaves are not produced on the apical portion, 

 which eventually forms the fruit. It may often be observed 

 that the cells of the base in these leaves multiply for a much 

 longer period than those of the apex. 



i The lateral portions of the undermost oldest parts of the 

 common stem of Rebouittia hemispherica extend consider- 

 ably forwards ; they close together so as to form a very 

 narrow, linear fissure in front of the transversely oval chan- 

 nel, and they amalgamate with the prominent lateral por- 

 tions of the fore edge of the shoot upon which the fruit- 

 stem is situated. The outer surface bears connivent leaves 

 above the apex of the rudiment of the inflorescence. The 

 longitudinal channel of the under side of the fruit- stem does 



