THE BRYOPHYTA: HEPATICAE, THE LIVERWORTS 401 



are smooth-walled, the others show a large number of minute thickenings 

 or tubercles which project from the walls into the lumen of the rhizoid 

 cells. The smooth rhizoids emerge from behind the amphigastria and 

 penetrate the soil. The tuberculate rhizoids lie parallel to the underside 

 of the thallus and form a system of conducting strands leading forwards to 

 the growing point, where water is readily absorbed. It may be correlated 

 with this that Marchantia can grow in much drier places than Pellia can. 

 Damaged rhizoids may be regenerated, secondary and even tertiary rhizoids 

 proliferating within the primar\' one. 



Vegetative Reproduction 



There are two methods of vegetative reproduction in Marchantia. The 

 first depends upon the ageing of the vegetative cells. It appears that the 

 cells of the thallus only live for a month or two, and as new cells develop at 

 the apices of the branches those further back die and eventually disorganize. 

 In this way the individual branches become separated, and each continues 

 life independently. 



The second method of vegetative reproduction is by means of gemmae. 

 These gemmae are lens-shaped masses of cells, which when detached develop 

 into new plants. They are developed in the base of small cup-shaped organs 

 termed cupules, which are produced along the midrib (Fig. 383). The 



Gemmae 



Thallus 



Fig. 383. — Marchantia polymorpha. Vertical section through 

 gemma cup containing gemmae. 



gemmae arise from a superficial cell which divides into two. The upper cell 

 enlarges and divides further to produce a group of cells with an indentation 

 at each end which marks the presence of a growing point. When mature 

 the gemma is liberated by the disorganization of the stalk formed by the 

 basal cell (Fig. 384). On its liberation the gemma develops into a fresh 

 thallus, growing from both ends simultaneously. Gemma formation usually 



14 



