280 FRESH-WATER ALG^E OF THE UNITED STATES. 



Specimens of this species have been reported to me from waters 

 beyond the Rocky Mountains, as large as a man's fist. 



Have endeavored to cultivate this Nostoc to get it to develop 

 the higher plant of which it is probably an intermediate stage 

 or condition, but failed. They did separate, multiply, and re- 

 multiply, merely reproducing, however, of their own kind in the 

 various stages of growth indicated above. The idea suggested 

 itself that water, possibly, is not a normal habitat ; they need an 

 occasional exposure to make them develop, as on dripping rocks, 

 moist wood or earth, trunks of trees in wet seasons, and the like. 

 On the banks of ponds where N. pruniforme occurs, there Scyto- 

 nema is also found, but did not succeed in tracing the immediate 

 connection between the two. 



The form known as N. commune. Vauch., is widely distributed 

 and appears in conditions as variable as the localities in which it 

 is found. It has been described under numerous names ; some- 

 times appearing on damp or wet ground in small thalli, but 

 these soon enlarge, and then flow together forming a soft ex- 

 panded stratum; sometimes bullate, membrane thickens and 

 hardens ; have seen the surface of the earth, after a rainy season, 

 acres in extent, dotted over with olive black, thin, dried mem- 

 branes, somewhat coriaceous fronds, an inch more or less in 

 diameter, a condition of this Nostoc; these membranes, after a 

 good soaking, show their true character. A striking instance 

 of personal observation occurred on the island of Anastatia, 

 Florida. Capt. J. D. Smith, a faithful collector in Florida, sent 

 me fresh specimens developed under favorable circumstances ; 

 they were parts of thalli which were inflated even to the size of 

 a man's head. Among the numerous specimens examined the 

 majority gave more or less evidence of a disposition to develop 

 a filamentous plant a Scytonema. Have transferred a few of 

 these to paper, Plate CXCVII, fig. 8, a not infrequent form of a 

 thallus ; fig. 9, normal form of filaments ; figs. 10, 11, cells of 

 filaments separated and forming young plants ; figs. 12-15, forms 

 of newly developed plants ; figs. 16, 17, filaments, one part 

 moniliform, unchanged, and the other part changing or already 

 developed to twice the diameter. 



Two French algologists, Messrs. Bornet and Thuret, published 

 a few years since a synopsis of the Nostocs. They were guided 

 by the old notion that they are really fully developed plants. 

 They made eight groups, which we transcribe somewhat modi- 

 fied and adapted to our forms as still useful in our present im- 

 perfect knowledge of the full life-history of these spurious forms. 



