NEW MYXOPHYCEAE FROM PORTO RICO 



63 



No resting spores have been observed in the material of this 

 species of Nostoc. Some of the colonies, however, are mature 

 and have formed hormogonia with deiinite individual teguments 

 showing the beginning of new colonies. After having been dried, 

 the color seems to diffuse out of the trieliomes into the tegument 

 when wet. 



Nostoc album sp. nov. 



Thallus spherical, up to 500 m diam., very smooth on the sur- 

 face ; trichomes tortuous, but not congested, bright olive-green to 

 violet; cells subspherical or dolioform, very finely granular; 

 heterocysts spherical, 6-7.4 m diam., single, fairly abundant; 

 tegument almost transparent, firm. 



Growing among moss near a stream in the vicinity of Mari- 

 cao, no. 1149, type. 



It is possible that the above-described new species of Nostoc 

 may be the juvenile stage of another species. The colonies are 

 in all stages of development from short filaments with only a few 

 cells to colonies up to one-half millimeter in diameter. There is 

 considerable indication that the largest colonies are nearing ma- 

 turity, as some of them show the formation of hormogonia. I 

 was unable to discover any resting cells, but the fact that among 

 the numerous very young colonies there is no indication that 

 any of them originated from resting cells leads me to conclude 

 that possibly there is no formation of single resting cells and 

 that reproduction takes place only by formation of hormogonia. 



More observations on the life history of the organism will 

 be necessary to establish its specific status. 



Nostoc simulans sp. nov. 



Thallus of no definite shape, more or less confluent, soft and 

 gelatinous ; trichomes moderately tortuous, constricted at the 

 dissepiments, 2.4-2.6 p diam., 1.5-2 times as long as the diameter; 

 heterocysts spherical, about 3 n diam., resting spores cylindrical 

 to ellipsoidal, 3.8-4.2 [i diam., 6.8-7.5 [i long, walls smooth, 

 hyaline. 



Growing in cavities in the wall of a house in Maricao, wo. 

 1117, type. 



The species proposed here belongs to the section Humifusa 

 of Bornet and Flahault, as a close relative in all appearances tc 

 humifnsum Carmichael. 



