THE MARCHANTIAS 



407 



divided into three orders — Marchantiales, Jungermaniales, and 

 Anthocerotales. 



The Marchantias. — The Marchantiales include the best 

 known Liverworts, among which are the Marchantias, the most 

 highly specialized Liverworts of this order and the family after 

 which the order is named. The Marchantia common in the north 

 temperate regions is Marchantia polijmorpha. It grows in moist 

 places, often occm-ring abundantly in swampy regions, on shaded 

 river banks, and on protected rocky ledges. It often gets started 



Fig. 363. — A female and a male plant of Marchantia polymorphia, show- 

 ing the external features of the plant body (about natural size). The two 

 plants, of which A is the female and B the male plant, differ most noticeably 

 in the character of the gametophores which are the erect stalks with expanded 

 tops (conceptacles) on which the sex organs occur, r, rhizoids; c, the gemmae 

 cups which are concerned with vegetative multiplication. 



in greenhouses where it develops and spreads rapidly on moist 

 soil that is left undisturbed. Being easily obtained, it is one of 

 the Liverworts most commonl}'^ studied in botanical laboratorieSo 



The plant body is shown in Figure 363. The flat, lobed, green 

 plant body or thallus lies prostrate on the substratum. Often 

 the plants are so much crowded as to overlap, and form aggrega- 

 tions that cover the substratum like a carpet. 



Single plants are often several inches in length and breadth, 

 and consist of a number of layers of cells in thickness. On the 



