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 isnamed. The Marchantia common in the north 
temperate regions is Marchantia polymorpha. It grows in moist 
places, often occurring abundantly in swampy regions, on shaded 
river banks, and on protected rocky ledges. It often gets started 
Fic. 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. 1, 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 commonly studied in botanical laboratories. 
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 
