Grinnellia americaita, Harv. 5 



texture of frond the mature tetrasporic plants are very similar 

 to the cystocarpic, but the decided contrast between the rough, 

 shapeless, tetrasporic incrassations and the smooth conical 

 cystocarps, easily enables one to distinguish them unaided by 

 the microscope. Each incrassation contains from four to forty 

 tripartite tetraspores, which closely resemble the carpospores. 



Habitat. 



Grinnellia has been described by Dr. Harvey as an Alga 

 growing ' on stones and shells in four or five fathoms of water.' 

 In the collections of Grinnellia made at Woods Hole and 

 Nantucket it was found growing abundantly on the piles of 

 wharves, at a depth of one to one and a half fathoms below 

 high tide-mark. After severe storms it frequently drifts ashore 

 in company with many other Algae which are torn from the 

 slightly submerged rocks and shells. 



Along the Massachusetts coast it thrives best in quiet waters, 

 though fine specimens are seen on rocks and shells submerged 

 one to two fathoms in the ' holes ' connecting adjoining bays 

 and indentations, through which the tidal currents run at 

 a speed of eight to ten miles an hour. Mr. Isaac Holden 

 has kindly allowed me to quote from his observations of this 

 Alga made at Bridgeport, Conn., where it attains very con- 

 siderable dimensions, his largest mounted specimens giving 

 the royal measurements of 25 cm. wide by 6^ cm. long. He 

 says he has found it growing in strong tide-currents, but that 

 it acquires its most luxuriant growth in quiet waters, thus 

 corroborating the observations made along the Massachusetts 

 coast. He has collected it from just below low water-mark 

 to the depth of six fathoms, and has secured many fine 

 specimens from the bottom, when wading at low tide, bring- 

 ing with them the stones or shells, particularly oyster-shells, 

 to which they were attached. Early in August adult plants 

 are very apt to become detached and float in large numbers. 

 From this last observation it appears that the mature plants 

 afford their spores a rapid and wholesale method of distribution. 



