(rarely only one). Leaves abruptly pointed. It has been thought 

 that this species was peculiar, in that the " lumen " extended 

 into the very point, but the tips vary in the leaves of the same 

 plant, so that this peculiarity cannot be considered a constant 

 characteristic of the species. The fruit appears later than that 

 of N. flexilis, and is less frequently found ; it differs from this 

 species also by being dia'cious. Antheridia, variable in size, 

 rarely exceeding 800 //. in diameter. Oogonia usually aggre- 

 gated (i to 3) ; tips of the enveloping cells becoming swollen ; 

 coronula evanescent ; mature oospore nearly or quite black 

 (thin sections reddish under the microscope), with 6 or 7 prom- 

 inent and thick ridges (striae), 34 to 36 JJL long, 30 to 34 // broad. 

 The spores are mature in July or August. The surface of the 

 mature nucleus is perfectly smooth, even under high amplifications. 



LOCALITIES. This species has been collected in Canada, 

 Macoun ; So. Framingham, Mass., Dr. Sturtevant (only anthe- 

 ridia seen ; hence determination doubtful) ; New Hampshire, 

 Saco Lake and Ammoneesie River (E. Faxon), notch of White 

 Mountains (O. D. Allen) ; New York, Edmunds ponds, Adrion- 

 dacks (T. F. Allen) ; Pennsylvania, Lehigh River (E. A. Rau) ; 

 California, San Bernadino (Parish Bros.) ; Oregon, Salem (E. 

 Hall) ; Nevada, Truckee Valley (S. Watson) ; Louisiana (Drum- 

 mond) ; Texas (Lindheimer) ; Mexico (Linden, 1840). 



EXPLANATION OF PLATES. The photograph is from an 

 elongated and loose form collected in Saco Lake, N. H. (Faxon), 

 natural size. The lithograph shows at i, a plant of natural size, 

 somewhat condensed above ; 2, aggregated oogonia, showing the 

 swollen tips of the enveloping cells, coronula already fallen, x 

 25 ; 3, antheridia, x 25 ; 4, nucleus, with 7 prominent and thick 

 ridges, x 50 ; 5, a minute portion of the surface of the membrane 

 of the ripe oospore, highly magnified ; surface between ridges 

 smooth. (The leaves in Fig. 3 are somewhat acuminate ; this is 

 rarely the case ; the tip in Fig. 2 shows the normal shape). 



NITELLA OBTUSA, Spec. nov. N. monarthrodactyla, homceophylla, 

 dioica, gymnocarpa, foliis apiculatis vel obtusis, membrana oosp'oro: 

 granulata. 



Description. Plants densely tufted, 20 to 25 cm. in height, 

 leaves of the lower verticils, sterile longer than the internodes, 

 3 to 5 cm. long, verticils composed of six (or seven) leaves ; 

 leaves all similar, once divided, terminal leaflets of sterile leaves, 





