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 



