236 BOTANICAL GAZETTE : [MARCH 
Size of prothallia 
Prothallia bearing antheridia vary much in size at the time of 
maturing their first sperms. Examples of plants composed of but 
few cells and with mature antheridia (figs. 4, 20) are not uncommon; 
on the other hand, many reach a width of 1-2 mm. before producing 
their first antheridia. The dwarf antheridial plants never attain 
any great size; they are but one cell in thickness, and never pro- 
duce archegonia. Fig. 41 shows the prothallium in fig. 20 and 
another taken at the same time from the same part of a culture 
and drawn to the same scale. These were just maturing their first 
antheridia. Antheridia are quite evenly distributed over the lower 
surface of the older portions of the large prothallia, and over the 
lower surface and mar- 
gins of the dwarf forms 
(figs. 4, 12a, 20). Fig. 
12a shows the abun- 
dance of antheridia on 
the large plant in fig. 12. 
Occasionally antheridia 
i rowths of 
Fic. 41.—Two prothallia of same age (as indi- ginal outg llia (6 
cated by maturity of first antheridia) and from large pr othallia (ng. 
same bit of soil; x28. 21a). Five months old 
antheridia and archegonia, are sometimes 4 mm. wide. They 
are strictly dorsiventral, although they show a marked tendency 
to take an upright position. The margins are distinctly crisped 
and plicate. After six to eight months, the marginal growth of 
the plants continues and the older portions die away much as in 
the liverworts. 
The rhizoids develop regularly from the lower surface of the 
prothallia, and are most abundant on the central part of the older 
portions, that is, at the base of the plant. They are long, slender, 
and sparingly branched near their free ends. The photographs 
reproduced in pl. XIII give a general idea of their character. ihe 
only point worthy of note is that mentioned above in connection 
