Grinnellia americana, 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 65 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. 
