194 PHYLUM IV. SIPHONOPHYCEAE 
The oogone and its covering now become thicker-walled 
and constitute a spore-fruit. The latter soon drops off 
and falls to the bottom of the water, where it remains at 
rest for a time and later germinates by sending out a 
jointed filament, which eventually gives rise to a branch- 
ing plant like the original. 
296. About 160 species of Stoneworts are known, all 
included in the single order Charales. The two families, 
Nitellaceae and Characeae are separated by the structure 
of the crown, which is 10-celled in the former, and 5- 
celled in the latter. The principal genus of the first 
family is Nitella, and of the second Chara; each contains 
in this country a dozen or more widely distributed 
species. 
297. Summary. The attempt has been made in the 
foregoing pages to treat the coenocytic plants in accord- 
ance with the theory that they have been derived from 
the many-celled filamentous algae of the Ulothrix type 
in the Phylum CHLOROPHYCEAE, where the segments of the 
filaments are true cells, each having a single nucleus. 
And it is regarded as probable that the coenocytic struc- 
ture was gradually attained by the formation of fewer 
and fewer partitions in the succession of filamentous 
plants. 
298. Accordingly the Cladophoraceae are given place 
at the beginning of the phylum, and they are regarded 
as having given rise to two general lines of development, 
one of which is characterized by the retention of a dis- 
tinctly filamentous structure, while in the other the 
coenocyte undergoes great differentiation into ‘‘root,” 
“stem” and ‘‘leaves.”” If we designate these lines by 
their highest holophytic representatives, we may call 
them (1) the Vaucheria line, and (2) the Chara line. 
299. In passing from Cladophoraceae to Vaucheriaceae 
