120 MCALLISTER: MORPHOLOGY OF THALLOCARPUS 
Flemming’s solution gave perhaps the most successful fixation, 
though there was no marked difference in the action of the killing 
solutions used. The gelatinous material of the older sporophytes 
interfered greatly with the penetration of the reagents, though an 
air pump was used to hasten the penetration of the liquids. 
The thallus of Thallocarpus varies greatly in size. Mature 
sporophytes may be found in thalli with a diameter of but two 
millimeters, while in late spring sterile thalli may be found which 
have a diameter as great as fifteen millimeters. The male plants 
rarely exceed three or four millimeters in diameter, the average 
diameter being less than three millimeters. 
When very young the thallus is distinctly bilobed, having 4 
single distinct growing area. The mature male plants are usually 
bilobed only. The female thalli usually become symmetrically 
four-lobed but later the lobing becomes less regular and in the | 
larger thalli there is often a suggestion of palmate lobing with the 
lobes often crowded and overlapping. : 
The thallus is very spongy in texture, resembling in the 
respect the spongy Riccias. Many irregular openings are visible 
in the upper surface. As is the case with the spongy Riccias the 
thallus is pale green in color. Superficially it resembles Ricca 
crystallina L. 
Cross sections of the thallus show it to be made up, in the 
upper part of the thallus, of irregular plates of cells, mostly 4 
single layer in thickness. At the upper surface these plates are 
broadened greatly to form the upper “epidermis” (FIG. 1)- The 
tissue at the base of the thallus is compact with but few intef- 
cellular spaces. 
The archegonia begin development at the surface of the thallus 
just back of the growing point. The mother cell of the arche- 
gonium elongates and divides transversely, the upper cell beims 
the smaller (FIG. 2). The lower cell divides again by a transvers€ 
wall (Fic. 3) which according to Campbell (6) also occurs in the 
development of the archegonium of Sphaerocarpos while in Rice 
this cell remains undivided. The divisions of the upper cell 
seem to be the same as in Riccia. The general structure of the 
mature archegonium does not present anything new. The neck 
canal cells seem to number four or five (Fics. 4, 5). | 
