THE GREEN ALGAE OF NORTH AMERICA 371 



2. G. HOLDENII Collins, 1897, P- 95, PI- IV. B., figs. 1-3; 

 P. B.-A., No. 316. Filaments 12-50 /. diam., cells irregular in 

 shape, oval, cylindrical or polygonal, terminal cell cylindrical 

 or tapering ; sporangia ovoid with elongate base, 100X30 p.. In 

 Unio shells, in fresh water. Conn. 



The large irregular cells distinguish this from G.polyrhiza. 



Family 3. VALONIACEAE. 



Frond originating in a vesicular or clavate cell of limited 

 growth, in all but the lowest forms branching or dividing into 

 many cells, which may be irregularly arranged, or may form 

 symmetrical, sometimes netlike fronds. Intercalary cell divi- 

 sion by ordinary wall formation is not common ; new cells arise 

 generally by an outgrowth from the parent in a way that leaves 

 some doubt as to whether the new cell should not be considered 

 as a new individual, or else by the closing in of annular con- 

 strictions of the frond. All marine, chiefly plants of warmer 

 waters. 



Oltmanns, 1904, p. 255, removes from this family the genera 

 Stphonocladus, Chamacdoris and Struvea, to form the family 

 Siphonocladiaceae. The main distinction seems to be the pres- 

 ence of a distinct axis in the latter. If we follow Borgesen, 

 1905, p. 288, and remove from Siphonocladus S, membranaccns 

 and its allies, this genus and the remaining genera of the family 

 agree in the presence of an original upright cell of limited 

 growth, and in the absence or rarity of intercalary division of 

 the cells by cross walls ; there would seem to be no need of 

 dividing the family. 



KEY TO THE GENERA OF VALONIACEAE. 



i. Frond always unicellular. i. HAIJCYSTIS. 



r. Mature frond pluricellular. 2. 



2. Original cell constituting a stipe different in character from the 



rest of the frond. 3- 



2. All cells similar to the original. 4. 



3. Stipe crowned by a network. 6. STRUVEA. 



3. Stipe crowned by a dense tuft of filaments. 5. CHAMAEDORIS. 



4. Daughter cells arising from the surface of the mother cells. 



2. VALONIA. 

 4. Entire contents of cell dividing into numerous smaller cells, each 



of which may develop like the mother cell. 5. 



5. Erect or tufted, not calcified. 3. SIPHONOCLADUS. 



5. Forming an adherent disk ; somewhat calcified. 



4. PETROSIPHON. 



