d16 LIFE-HISTORIES 
Fic. 340, I.—Umbrella-liverwort (Marchantia polymorpha, + Umbrella- 
liverwort Family, Marchantiacee). Male plant bearing antheridia- 
carriers (antheridiophores) ?. (Atkinson.)—The plant is common on 
moist earth, rocks, ete., throughout the world. 
Fig. 340, II1.—Umbrella-liverwort. Top of antheridiophore (%), cut ver- 
tically to show the cavities containing antheridia. (Atkinson.) 
body is carried away by some current of ‘rain water and comes to 
rest in a favorable spot it sends out pseudo-roots from whichever 
surface happens to be undermost, and begins to grow into a new 
thallus. After a while organs distinctive of the sex appear near the 
growing end, and curving upward become differentiated into a 
cylindrical stalk and an expanded top. In male plants (Fig. 340 
I-IV) this top is a lobed disk on the upper side of which are pits, 
each containing a multicellular gametangium, from which come 
stender motile gametes like those of Riccia already described. 
Archegonia arise also on the top of what is at first a somewhat similar 
