124 PLANT-LIFE 



which, to the casual observer look like flimsy flakes of 

 green tissue. R.fluitans, with other submerged species, 

 is sterile so long as covered by water; it fruits only when 

 exposed to the air. The thallus in this Order may be 

 lobed or branched ; it is furnished with delicate rhizoids, 

 proceeding from the under-surface, by which it is at- 

 tached to its substratum. The rhizoids are not roots. 

 The structure is of the simplest type found among the 

 Liverworts. The male and female organs occur in sunk 

 chambers on the upper side of the thallus. The fertilized 

 egg-cell becomes a stalkless spore capsule containing 

 spores. 



The Marchantiacece. — Somewhat over 160 species are 

 known to science. The members of this Order are in 

 every way an advance upon the Ricciaceae, and the 

 structure is frequently distinctly complicated. It is 

 proposed to devote a little space to a study of a very 

 common species, in order that the reader may the better 

 grasp the life-story of a fairly representative Liverwort. 



Marchantia polymorpha grows freely on damp soil 

 and in damp places generally; it may be found on old 

 walls, on the walls of hot-houses, and even in plant- 

 pots ; its life-history is fully illustrated on Plate IV. 

 The thallus — i.e., the gametophyte — is flattened and 

 prostrate; it is deeply lobed, and produces two-lobed 

 branches ; the margin is wavy. There is an inconspicuous 

 midrib, and rhizoids, proceeding from the under-surface, 

 attach the thallus to its substratum, some of them 

 serving as water-conductors. There are scales, con- 

 sisting of a single layer of cells on the under-surface; 

 while the upper surface is marked out in diamond-shaped 

 areas, in each of which there is a central pore, leading 



