430 
IOWA ACADEMY OF SCIENCE Vol. XXIV, 1917 
cell is given over to the formation of archegonia, which are ter- 
minal, while in the second group, to which Blasia belongs, the 
archegonia are formed on the dorsal side of the thallus from 
segments cut off from the apical cell, so that apical growth is 
not hindered. The subfamily Codonioideae includes eight genera, 
of widely divergent variations, namely Pellia, Calyeularia, 
Treubia, Fossombronia, Noteroclada, Petalphyllum, Siniodon, 
and Blasia. The genus Blasia, according to Sehiffner 5 includes 
but one species B. pusilla. 
It is distinctly transitional between thallose and foliose forms 
of Hepatics, having a flattened, elongate thallus, which lies 
prostrate and firmly anchored to the substratum by rhizoids for 
about three-fourths of its length. The apical regions are free 
and grow somewhat inclined although the plants almost always 
point down the slope. The thallus is characterized by dich- 
otomous branching and has a broad midrib extending through- 
out its entire length on the underside. Along the midrib the 
thallus lobes are inserted horizontally and laterally. They re- 
semble leaves but are termed thallus lobes, not being separated 
from the midrib and from each other. 
This dorsi-ventral thallus is relatively simple, the tissue be- 
ing for the most part composed of uniform cells with thin walls. 
Chloroplasts are numerous in all the cells with possibly a few 
more in the top layer than in the lower ones. No air-chambers 
or pores were found. In cross section the thallus shows wing- 
like extensions projecting out from the midrib, which is found 
on the underside. This midrib, slightly depressed on the dorsal 
surface, and bowed out on the ventral side, is eight to twelve 
cells* in thickness and from the midrib to the point of lobe in- 
sertion, the thallus narrows gradually to the margin of the 
wings, which are one cell in thickness (1, figure 84). 
The only differentiation in the structure of the thallus tissue 
was first noticed in cross section, where groups of cells vary- 
ing from nine to thirty-six in number stained more deeply than 
the surrounding tissue. This differentiation suggested a strand 
of cells set apart for some special purpose, probably to function 
in conduction. Conducting tissue has been reported in three 
of the Ana (irogv nous Jungermanniales and nowhere else in the 
Liverworts. Sir William Hooker 1816 discovered the strands in 
Juogermannia now Pallavicinia Lyellii. Gottsche in 1864 de- 
