MORPHOLOGY OF BLASIA PUSILLA 
435 
Ventral Differentiations . — The two-celled mucilage hairs, 
found on both sides of the th alius, originate from a superficial 
cell which pushes out from the surface. This cell divides once 
and the basal cell retains its nucleus and chloroplasts while the 
outer one breaks down into a mucilaginous substance which 
stains very deeply. These hairs usually turn inward toward 
the apical cell, and form a protection for the growing point and 
for the younger sex organs which are found near the apex. The 
mucilage hairs do not seem to be deciduous, for old ones are 
found far back on the thallus after the growing shoot has 
elongated and formed new hairs at its tip. 
The ventral side of the thallus develops smooth, unicellular, 
colorless rhizoids. These hairlike structures are merely out- 
pushings of the epidermal cells along the midrib, which function 
both as anchorage organs and water absorbers. They are often 
so numerous that they form thick mats along the midrib, and the 
plants can be lifted from the soil only with difficulty. 
The under leaves are scalelike appendages called amphigastria. 
They are usually several cells in thickness at the center and one 
cell thick at the margin. These scales have denticulate margins 
in contrast to the entire margin of the thallus. They are easily 
detached and may give rise to new plants. No doubt the amphi- 
gastria are rudiments of the ventral row of leaves commonly 
found in the leafy liverworts, and may assist in holding water. 
We have a final ventral differentiation in the leaf auricles. 
These appendages begin as plates of cells pushed out from the 
lower epidermis of the thallus. Their marked incurving pro- 
duces a hollow, globular structure which becomes filled with 
Nostoc. As the cells are pushed out a mucilage papilla is formed 
at the outer margin which gradually curves inward. Another 
mucilage papilla pushes out from an epidermal cell into the 
hollow already formed. After the formation of the leaf auricle, 
it is infected with Nostoc which finds entrance at the point 
where the mucilage hair touches the thallus. In the young 
stages we find an aperture here but later the auricle is completely 
closed. Seen from the top of the thallus the .Nostoc colonies ap- 
pear as tiny black spots imbedded in the tissue. 
At the time Schmidel 13 studied Blasia there was some uncer- 
tainty as to what the Nostoc might be. Schmidel in his “Dis- 
sertatio cle Blasia” considered the auricles as antheridia and the 
individual cells as sperms. 
