84 Minnesota Algae 



Canada. On floating balls of Polysiphonia. Pictou Harbor, Nova 

 Scotia. (Mackay). Maine. Forming slimy patches on wharves. Eastport. 

 (Farlow). Massachusetts. Wood's Holl. (Farlow). 



Genus TRICHODESMIUM Ehrenberg. 

 Ann. Physik. u. Chemie. i8: 506. 1830. 



Plants forming scale-like, disconnected, free-floating colonies quickly 

 dissolving into mucous; trichomes cylindrical, without sheaths; apex of 

 trichome straight, tapering, slightly capitate; apical cell truncate-conical, 

 furnished with a convex calyptra. 



Floating in great abundance in the ocean, especially in equatorial re- 

 gions. 



I Trichomes straight. T. erythraeum 



II Trichomes flexuous or spirally twisted. 



1 Colonies up to 6 mm. in length; trichomes 7-16 mic. in diameter, not 



constricted at joints, those in center of colony having the form 

 of twisted ropes, free at the ends T. thiebautii 



2 Colonies spirally twisted, light yellow; trichomes 16-25 niic. in diame- 



ter, twisted together into cords. T. contortum 



170. Trichodesmium erythraeum Ehrenberg. Neue Beobachtungen uber 



blutartige Erscheinungen in Aegyptien, Arabien und Siberien. In 



Poggendorf. Ann. Physik. u. Chem. 18: 506. 1830. Gomont. Monogr. 



Oscill. 216. pi. 5. f. 27-30. 1893. De Toni. Syll. Algar. 5: 202. 1907. 



Montagne. Memoire sur le phenomene de la coloration des eaux de la 



Mer Rouge. Ann. Sci. Nat. Bot. III. 2: 360. pi. 10. f. d. 1844. (T. hindsii). 



Plate IV. fig. 40. 



Colonies very short, scarcely i mm in length, purplish red (when dried 

 grayish green or dark brown); trichomes 7-1 1, rarely up to 21 mic. in 

 diameter, straight, parallel, constricted at joints, the more slender ones 

 with apices gradually tapering, the larger ones with apices very briefly 

 tapering; cells 5.4-11 mic. in length; cell contents coarsely granular. 



Central America. In dense masses of a beautiful red color, on surface 

 of ocean. The odor was pronounced and very disagreeable. San Salvador. 

 14° lat. N. April 1837. (Hinds). 



It is interesting to note that it is the presence of this alga which has 

 caused the Red Sea to be so named. 



171. Trichodesmium thiebautii Gomont. Essai Class. Nostocacees homo- 



cystees. Morot. Journ. de Bot. 4: 356. 1890; Monogr. Oscill. 217. 

 pi. 6. f. 2-4. 1893. De Toni. Syll. Algar. 5: 203. 1907. 



West Jun., W. Some Oscillarioideae from the Plankton. Journ. of Bot. 

 37: 337. 1899. Lemmermann. Algenfl. Sandwich-Inseln. Bot. Jahrb. 34: 

 618. 1905. 



Plate IV. fig. 41, 42. 



Colonies up to 6 mm. in length (in dried material dark green); trich- 



