[Chap. XLVIII 



MOSSES AND LIVERWORTS 



653 



As an example of the foliose liverworts, Porella may be studied. It is 

 common on tree trunks, on rocks, and even on walls of buildings. The 

 novice often mistakes it for a moss. Its curved reclining stems bear three 

 rows of flattened leaves, two on the dorsal side and one on the ventral 

 side. 



Vegetative propagation occurs in liverworts by fragmentation, by 

 "brood bodies," and by gemmae formed in variously shaped gemmae- 

 cups. These are small cup-shaped outgrowths from the upper epidermis 

 of the thallus. From the bottom of the cup numerous upright fiddle- 

 shaped green thalli develop. They germinate immediately when trans- 

 ported to the soil bv rain or wind. 



Fig. 303. \^egetative and reproductive structures of Marchantia: A, vegetative 

 propagules, or gemmae, in cupules on a portion of a thallus; B, part of a male 

 thallus with upright antheridial branches terminating in disk-like structures in 

 which antheridia and sperms develop; C, a female thallus with upright archegonial 

 branches terminating in radially branched structures in which archegonia and 

 eggs develop; D, diagram of a vertical section of the apex of an archegonial 

 branch to show location of the pendant archegonia; E, diagram of a vertical sec- 

 tion of the apex of an antheridial branch to show location of antheridia; F, form 

 of sperms; G, isolated sporophytes that have developed from fertilized eggs within 

 archegonia represented in D. Elongation of the sporophyte stalk pushes the 

 sporangium out of the archegonium, but the base of the stalk remains attached to 

 the gametophyte as it does in mosses. 



