THE GREAT GROUPS OF BRYOPHYTES 



gemmae fall off and develop new thallus bodies, making 

 rapid multiplication possible. 



MarcJiantia also possess remarkably prominent gameto- 

 phores, or "sexual branches" as they are often called. 

 In this case the gametophores are differentiated, one bear- 

 ing only antheridia (Fig. 96), and known as the "anthe- 

 ridial branch," the other bearing only archegonia (Figs. 97, 

 98), and known as the "archegonial branch." ^The scal- 

 loped antheridial disk and the star-shaped archegonial disk, 

 each borne up by the stalk-like gametophore, are seen in the 

 illustrations. Not only are the gametophores sexually dif- 

 ferentiated, but as only one appears on each thallus, the thal- 

 lus bodies are sexually differentiated. When the two sex 

 organs appear upon different individuals, the plant is said to 

 be dioecious, meaning "two households"; when they both 

 appear upon the same individual, the plant is monoecious, 

 meaning " one household." Some of the Bryophytes are mo- 

 noecious, and some of them are dioecious (as Marchantia). 



Another distinguishing mark of the line of Marchantia 

 forms is that the capsule-like sporogonium opens irregu- 

 larly to discharge its spores (Fig. 97, 7). 



70. Jungennannia forms. This is the greatest line of 

 the Liverworts, the forms being much more numerous 

 than in the other lines. They grow in damp places ; or in 

 drier situations on rocks, ground, or tree-trunks ; or in the 

 tropics also on the leaves of forest plants. They are gen- 

 erally delicate plants, and resemble small. Mosses, many of 

 them doubtless being commonly mistaken for Mosses. 



This resemblance to Mosses suggests one of the chief 

 features of the line. Beginning with a simple thallus, as 

 in the Marchantia line, the structure of the thallus re- 

 mains simple, there being no such differentiation of tissues 

 as in the Marchantia line ; but the form of the thallus 

 becomes much modified (Figs. 99, 100). Instead of a flat 

 thallus with even outline, the body is organized into a cen- 

 tral stem-like axis bearing two rows of small, often crowded 



