6 BULLETIN 1191, U. S. DEPARTMENT OF AGRICULTURE. 
pear to be single isolated cells. (Fig. 2, E and F.) Careful exami- 
nation of isolated specimens, however, reveals the presence of one or 
more additional cells. The cell which is to give rise to the new plant 
or embryo is much larger than the other cells of the filament in 
which it occurs. It-also develops denser, more deeply colored con- 
tents. The appearance and behavior of this cell, which may be 
‘alled the proembryo, strongly suggest sexual origin, but that it is 
of this nature awaits proof. As the proembryo approaches ma- 
turity, it takes on the form of a truncated cone attached to the sub- 
stratum by the expanded, thin-walled base. The walls next the free 
end b-come very thick, but remain thin over the summit. The cell 
contents become congested at the free end of the cell, chromatophores 
becoming longitudinally oriented. (Fig. 2, G and H.) The pro- 
toplast now begins to withdraw from the base of the cell, a new 
cell wall is formed around it, and the extrusion of the embryo takes 
place. The thin-walled summit of the proembryo opens and the 
now spindle-shaped embryo is thrust out by the rapid absorption 
of water. The embryo is not forced violently out, but remains with 
its tapering base within the thick-walled mouth of the empty pro- 
embryo, which serves as a holdfast until the embryo can form 
rhizoids or rootlets. (Fig. 2, I.) 
A cross-wall is formed, dividing the embryo into a two-celled 
structure at the time when it is being extruded. Other cross-walls 
appear in rapid succession until the embryo is 5 or 6 cells long. The 
first rootlet or rhizoid now buds out from the base of the embryo. 
grows down through the empty proembrvo cell, and attaches the 
embryo to the substratum. Additional cross-walls are formed in 
the embryo until it is 7 or 8 cells long, and then longitudinal walls 
begin to appear. Additional rhizoids, always consisting of a single 
hairlike cell, bud out above the primary one, increasing the grip of 
the young plant as it grows. (Fig. 2, J.) By the time the young 
plant is 12 to 15 cells long, the region of most active growth seems 
to become located near the base. Owing to difficulties experienced 
in growing plants in the laboratory, the later stages up to the 
origin of the stipe must be omitted for the pressnt. Plants have 
been brought to the embryonic stages in only a few instances, and 
when these stages are attained, the plants are much more easily dis- 
lodg d and lost than pre-embryonic plants. Thus, good cultures 
have disappeared completely while they were believed to be making 
a thrifty growth. From the results obtained, however, an estimate 
can be made of the time required for the different stages, and a 
notion can be formed of the conditions under which the young plants 
develop. Spores will germinate and live for many days under con- 
ditions of temperature and stagnation that speedily prove fatal to 
jarger plants. It seems to be true that, as the young plant grows, 
it continually requires more and mor? air and a lower temperature, 
and, at the same time, the chance of its being dislodged seems to in- 
crease. In midwinter the second or embryonic stage may appear 
six weeks after germination of the spores. Sporelings germinated 
late in winter or in the spring from February to May grow much 
more slowly than those germinated in December, apparently re- 
quiring several months to reach the embryonic stage. The long and, 
frequently, branching filaments described above occur mostly in 
summer and autumn, very few plants apparently developing good 
