106 



MANUAL OF BOTANY 



growing points are formed. Bach gemma is several cells thick 

 in the centre, but the layers thin out towards the margin, where 

 it is only one cell thick. T^^len it falls to the ground after 

 liberation from the cup, the lower surface puts out root hairs 

 and the upper takes on the structure already described. There 

 is at first no difference in structure between the two sides ; 

 whichever happens to come in contact with the ground becomes 

 the ventral one. The gemma contains chloroplastids. 



Marchantia is a dioecious form ; some shoots give rise to an- 

 theridia, others to archegonia. 



Both these organs are borne on special gametophores, which 

 spring from the upper surface of the thallus. The antheridiophore 



Fia. 864. 



Fig. 865. 



Fig. 8G4. Surface view of tbe so-called stoma of Marcbantia ( x 250). After 

 Kny. Fig. 865. Eeceptacle of Marchantia with gemmee, a. 



{fig. 866, ^ is a thick fleshy stallc which spreads out at the summit 

 into a somewhat flattened circular disc, which is lobed at its 

 margins. The disc has several growing points, each producing 

 antheridia, in acropetal succession, which are seated in de- 

 pressions on its upper surface. The surface of the disc contains 

 air-chambers lilt e those of the rest of the thallus. The antheridia 

 have the structure already described ; the depressions in which 

 they are seated are flask-shaped, and only communicate with 

 the exterior by a narrow canal. 



The archegoniophore is somewhat more complex. Like the 

 antheridiophore, it is a long stalked body, crowned by a disc. 

 The latter is not a flattened structure, bat consists of eight 

 arms or branches radiating from the centre of the stalk, sorne- 



