101 HOFMEISTER, ON 



is the case in Rebouillia and Targionia. Differences of 

 habit depend also upon the greater or less rapidity of the 

 expansion of the fore edge of the shoots during their 

 longitudinal growth, and, lastly, upon the fact whether the 

 older shoots die and moulder away with greater or less 

 rapidity. In Rebouillia hemispherica and Fegatella conica 

 they last for several years ; in Targionia and Marchantia 

 the decay of the older generation of shoots begins very 

 shortly after the complete formation of the next youngest 

 shoots. It often happens that almost every trace of the 

 (pseudo) furcate ramification of the plant is obliterated by 

 the fact of a new shoot being developed in one only of the 

 indentations of the fore edge of an older shoot, the other 

 new shoot, situated in the other indentation, becoming 

 abortive. This is often the case in Rebouillia and Tar- 

 gionia. The buds (bulbils according to Mirbel) of Lunu- 

 laria and Marchantia, which are formed in special 

 receptacles on the median line of the shoots, afford a 

 particularly striking example of the above species of rami- 

 fication. These receptacles are formed in the following 

 manner: — in the earliest stageof the shoot, cell-multiplication 

 commences, either all round the spot where the buds are 

 destined to be formed, or in a semicircular chain of cells 

 (the semicircle lying open to the front) of the upper side of 

 the shoot. This cell-multiplication gives rise in Mar- 

 chantia to an annular, in Lunularia to a horse-shoe shaped 

 cushion. The division by septa parallel to the surface, of 

 those cells of the upper side of the shoot which are enclosed 

 by the cushion, soon ceases, whilst it continues for some 

 time in the cells lying outside. Thus the space of the 

 upper surface which is enclosed by the cellular rampart, 

 and is destined to form gemmae, becomes a depression. 

 The margin of the wall grows in Lunularia into a delicate 

 membrane (PI. XV, fig. 19), consisting of a single layer of 

 cells. In Marchantia from sixteen to twenty teeth sprout 

 from it (PI. XV, figs. 1, V), which incline towards one 

 another when young, and thus cover the gemmae ; after- 

 wards they become upright. The history of the develop- 

 ment of these teeth is as follows : — every other cell of the 

 edge of the annular wall expands considerably outwards. 



