Ig15] HUTCHINSON—PELLIA EPIPHYLLA 139 
dichotomous; although the thallus may appear to have a central 
axis along the main line of growth, it is a matter of comparative 
rapidity in growth rather than origin. This form of apical cell 
is continued throughout the antheridial period. 
The fourth period of growth is terminal and regional; it is con- 
cerned with the production of the archegonial pocket. The cells 
surrounding the original apical cell assume the power of cutting 
off lateral and posterior segments. The region of growth is in the 
form of a terminal disk. Lateral segments are crowded out on all 
sides to produce the continuous, cup-shaped involucre. A cross- 
section in any plane is similar to a horizontal section through the 
growing region at the time of branching (fig. 49). This growth is 
checked by the production of archegonia; any of the surface cells 
of the pocket may produce an archegonium (fig. 40). About the 
time of fertilization the last period of growth begins. 
Any further growth is in connection with the developing sporo- 
phyte. Starch accumulates in the cells surrounding the foot and 
a massive growth takes place. Usually only one sporophyte 
develops in each pocket; a rather thick calyptra is formed about 
it, and sterile archegonia are carried along; these are to be seen 
attached to the surface of the calyptra. The first growth of the 
‘gametophyte is massive, similarly the last. 
Relation of antheridium and archegonium 
The relationship of the various forms of antheridia and their 
relation to the archegonium is demonstrated by the occurrence of 
antheridia in a single species, Pellia epiphylla, which are similar in 
development to each of these organs. The Marchantiales condi- 
tion is generally to be found among the first antheridia; the Junger- 
- manniales form is most dominant at the middle period, occurring, 
however, throughout the complete antheridial period. The arche- 
gonial form is usually found among the last antheridia to be pro- 
duced. There is an evident time relation between these forms. 
Moreover, one may be regarded as derived from another through 
a series of progressive sterilizations (text fig. 1).5 In the form 
‘Cf. Hormersrer, The higher Cryptogamia. Untersuchungen tiber die Leber- 
moose. Vol. II (Pellia). 
