370. A TEXTBOOK OF GENERAL BOTANY 
idium of a liverwort is usually somewhat oval and consists of an 
inner portion, composed of numerous sperm cells, surrounded by 
a single layer of sterile cells (Fig. 400). Each of the sperm cells 

Fre. 401. Immature sporophyte of Riccia 
within the archegonium 
The cells of the basal portion, or venter, of the 
archegonium have divided, so that this part of 
the archegonium consists of two layers of cells. 
At this stage the sporophyte consists of a con- 
siderable number of megaspore mother cells 
surrounded by a single layer of sterile cells. 
The nuclei and protoplasm are shown in the 
sporophyte and not in the tissue of the game- 
tophyte. (x 140) 
produces a single ciliated 
spermatozoid (Fig. 400). 
Fertilization takes place 
by the swimming of a 
spermatozoid to the egg in 
the archegonium and the 
fusion of the spermatozoid 
with the egg. Owing to 
the fact that the spermato- 
zoids have no other means 
of reaching the archegonia 
than by swimming through 
water, it is evident that 
water is necessary for the 
accomplishment of ferti- 
lization. This indicates 
that the Hepaticae are 
descended from an algal 
ancestor, which lived in 
water and in which ferti- 
lization was also accom- 
plished by means of motile 
spermatozoids. 
Sporophyte. The ferti- 
lized egg of the Hepaticae 
germinates immediately 
within the archegonium, 
but, instead of giving rise to a thallus, produces a structure in 
which spores are formed (Fig. 401). 
This spore-bearing strue- 
ture is known as a sporophyte. The spores, on germination, 
produce a gametophyte. The sporophyte, in its simplest form, 
consists of a single sporangium (Figs. 401, 402), while in 
most of the Hepaticae it is a sporangium with a stalk and 
