Life-History. 
23 
bricks exist. Amidst sucK an environment it 
rapidly makes lieadway, broadening until it even- 
tually assumes a heart-shape (Fig. 17), but seldom 
more than Jin. At this stage its lower surface be- 
comes partly covered with tiny root-hairs, each com- 
posed of a row of cells; there also, and along the 
edges are developed the sexual organs — antheridia 
being the male, and the archegonia (situated in the 
middle of the lower surface) the female organs. In 
this respect Ferns differ from most of their allies, 
Fig. 16. First growth of Fern Fig. 17. Lower surface of 
Fig. 18. Spirally coiled antherozoid (much magnified). 
where prothalli bear only male or only female 
organs. 
The antheridia are small protuberances com- 
posed of three comparatively large cells, originating 
as outgrowths of cells of the epidermis; each out- 
growth is cut off, as a new cell, by a cell-wall. In 
some prothalli, the contents of the cell thus formed, 
and containing a tissue of mucilaginous nature, 
break up into a number of small, rounded " parent 
cells," in each of which is formed an " antherozoid^^ 
a 
from spore, showing : p, 
prothallus ; rh, root=hairs ; 
and s, spore (much magni= 
fied). 
mature prothallus, show=« 
ing : a, female organs or 
archegonia ; rh, root=hairs 
(much magnified). 
