THE GREEN ALGAE OF NORTH AMERICA 197 



7. Cells 10-16 /u, diain. ; fronds usually inflated and constricted ; often of 



large size. 18. E. intestinalis. 



7. Cells 4-8 /x diam. ; fronds usually short. 8. 



8. Membrane 8-10 M thick ; cells 5-7 M diam. n. E. minima. 



8. Membrane 15-20 /* thick ; cells 4-5 /u, diam. 17. E. micrococca. 



9. Fronds simple, inflated and flexuous. 15. E.flexuosa. 



9. Fronds simple or with occasional proliferations ; not inflated. 10. 



9. Fronds regularly branched. u. 



10. Frond narrowly linear, strongly compressed. 



13. E. marginata. 

 10. Frond filiform, 2-8 cells wide, tubular only in the widest parts ; 



branches two cells wide. 3. E. torta. 



10. Frond filiform, tubular, of uniform diameter; of numerous series 



of squarish cells. 14. E. prolifera var. tubulosa. 



ii. Frond beset with numerous thorn-like branches. 



12. E. salina var. polyclados. 

 ii. Branches proliferous, similar to main filaments. 



14. E, prolifera. 



u. Branches of successive orders, tapering from base to apex. 12. 

 12. Chromatophore filling cell. 13. 



12. Chromatophore not filling cell, giving a net-like appearance. 



14. 

 13. Ultimate ramuli short, spine-like, not monosiphonous. 



9. E. ramulosa. 



13. Ultimate ramuli of a single series of cells. 6. E. crinita. 



13. Ultimate ramuli polysiphonous, of a few symmetrically placed 



series of cells. 7. E. erecta. 



14. Ultimate ramuli of a single series of cells. 4. E.plumosa. 



14. Ultimate ramuli not of a single series of cells. 



5. E. clathrata. 



i. E. PERCURSA (Ag.) J. G. Agardh, 1842, p. 15 ; P. B.-A., 

 Nos. 469, 968 ; Tetranerna percursum Areschoug, 1846, p. 192, PI. 

 II. A. Frond filiform, in the earliest state of one row, afterwards 

 of two rows of cells, placed symmetrically side by side ; cells 

 10-15 p. wide, from once to twice as long. Greenland to N. J. ; 

 Alaska to Cal. Europe. 



A common species, forming masses in upper tide pools, and 

 in ditches in marshes, etc. It often grows in company with 

 other species, but is easily distinguished on microscopic exam- 

 ination by th'e double row of cells, usually in exact symmetry, 

 side by side. The small chromatophores occupy only part of 

 the cell room, giving the same net-like appearance found in E. 

 clathrata. 



