294 TUFTS COLLEGE STUDIES, VOL. II, No. 3 



strongly developed ; erect filaments 6-10 p. diani. ; cells about 

 as long as broad, terminating in an inarticulate hair, or in an 

 ovate-ellipsoid cell ; sporangia terminal, clavate, 11-12X16-21 /u,. 

 Greenland. 



This species forms a continuous layer, in company with Calo- 

 thrix ; the subspherical gelatinous thalli distinguish it from the 

 other species of the genus. Under this should be included, ac- 

 cording to Rosenvinge, C. pellicula Kjellman, 1883, p. 286, PL 

 XXXI, figs. 4-7, which forms a thin slimy membrane on wood ; 

 Rosenvinge was unable to find the intercalary sporangia to 

 which Kjellman refers, and which, if confirmed, would require 

 the removal of the plant to another genus. 



22. MICROTHAMNION Nageli in Kiitzing, 1849, p. 352. 



Frond very minute, consisting of a branching, monosiphonous 

 filament, attached by a bulbous base ; stem and branches of 

 about the same size ; first partition in branch some distance 

 above base ; terminal cell blunt ; cells cylindrical, with thin 

 wall ; chromatophore a thin sheet, more or less completely 

 covering the cell wall, without pyrenoid. Asexual reproduc- 

 tion by ovoid, biciliate zoospores without stigma, germinating 

 immediately. 



A genus of very minute plants, the frond not reaching the 

 height of i mm. ; in appearance resembling a small Trente- 

 pohlia, but differing in that the spores are produced in any cell 

 of the filament, practically unchanged ; not in more or less 

 specialized sporangia. 



KEY TO THE SPECIES OF MICROTHAMNION. 

 i. Ramification dense; main stem and branches indistinguishable. 



i. M. Kutzingianum. 

 i. Ramification open ; main stem distinguishable throughout. 



2. J\f. strictissimum. 



i. M. KUETZINGIANUM Nageli in Kiitzing, 1849, p. 352; 

 Hazen, 1902, p. 191, PL XXVI, fig. i ; PL XXVII, figs. 2-4; 

 P. B.-A., No. 568. Up to 200 fj. tall, very densely and irregu- 

 larly branched, main stem and branches indistinguishable ; 

 ramuli one- to several-celled, patent or curved ; cells cylindrical 

 or slightly clavate, 3-4 ^ diam. in all parts of the frond, usually 

 2-4 diam. long, occasionally considerably longer ; chromato- 

 phore bright green, usually covering the entire cell wall. Fig. 

 83. Mass, to N. Y. Europe, New Zealand. 



Forming a thin coating on sticks, woodwork, etc., in streams ; 

 also in greenhouses. 



