232 FRESH-WATER ALG.E OF THE UNITED STATES. 



This genus has by some authors been incorporated into the 

 genus Mesocarpus, but the method of fruiting is so absolutely 

 distinct, prefer to keep it separated. 



PLEUROCARPUS MIRABILIS, A. Br. 



Diameter of vegetative filaments, 25-30 ^ ; cells 2-5 times 

 longer than the diameter. Spores somewhat depressed 

 globose, about the same diameter as that of the cells, hav- 

 ing a lateral position, mostly on one side of the filament at 

 the joint of the two copulating cells. 



Common everywhere; forms large, loosely interwoven 

 light green floating masses, usually only one to two feet in 

 diameter, but sometimes 20-30 feet across. The filaments 

 are very fragile, breaking into short lengths ; almost always 

 geniculately united, but never in fruit. Was familiar with 

 this form for eight years, saw it constantly, but always 

 sterile, and was coming to the conclusion that the story of 

 A. Braun about the mode of fruiting must be a myth, when 

 suddenly, in 1883, it w r as found in three distinct localities; 

 first by E. S. Cheeseman, Knowlesville, N. Y.; second by 

 Miss E. Butler, in a swampy meadow near Maiden, Mass.; 

 and third, by myself in a small pool on the border of a pond 

 familiarly know r n as Buckaberry Pond, in Northern New 

 Jersey. Have not seen it since. 



Syn. Mougeotia genuflexa, Ag. ; Conferva genuflexa, Dillw. ; Zygo- 

 goniumpleurospermum, Kg. 



Plate CXLIX, figs. 8, 9, two pairs geniculate filaments 

 grown together. The form known by earlier authors as 

 Mougeotia genuftexa. Fig. 10, the beginning of the formation 

 of a lateral spore ; figs. 11-13, three matured spores, the 

 result of lateral conjugation ; figs. 14, 15, sterile filaments. 



PLEUROCARPUS COMPRESSUS, Lyngb. 



This specific term, compressus, was applied by Lyngb., 

 Gray and Bab., and others to the form figured, Plate 

 CXLIX, figs. 10-13, and Mougeotia genuflexa to figs. 8, 9. 



PLEUROCARPUS COLUMBIANUS, Wolle. 



Diameter of filaments, 37-40 ^ ; cells 4-8 times longer than 

 broad, geniculately joined. In the year 1879, we an- 

 nounced this plant as a new species. Bull. Torrey Bot. 

 Club, January, 1879. It is nearly one-half thicker and the 

 cells are longer than those of P. mirdbilis ; would more 

 properly be named a variety of that species. 



Plate CXLIX, figs. 6, 7, sterile filaments. 



