1908] Collins,— Notes оп Algae. IX 159 
That the distinction has not before been made is not unnatural; 
our plant does not grow on small or loose stones, it seems to prefer 
the hardest rock, seldom occurring on soft or crumbling rocks, where 
it could be easily removed. It cannot be scraped off without reducing 
it to a shapeless mass, but a knife must be used, and unless special 
care is taken, the greater portion of the basal part is left on the rock. 
In material so obtained the difference between the basal part and that 
of P. cruenta is not noticeable. ‘The material distributed in P. B.—A., 
No. 899, is of this character; it is intended to distribute another lot, 
of more perfect material, which will show the identity with the P. 
M iddendorffii of the west coast, distributed as P. В.-А., No. 900. 
The tetraspores of Petrocelis are formed by transformation of cells 
of the upper part; in P. cruenta and P. Middendorffit one cell in a fila- 
ment is so transformed, rarely two cells. In P. Hennedyi (Harv.) 
Batters of northern Europe the tetraspores are seriate, often occupying 
a considerable portion of the filament; this species may occur with us. 
Unfortunately, spores in Petrocelis are rare, except in winter, which is 
not a pleasant time to collect on exposed shores at low water mark. 
The writer has examined specimens of Petrocelis from Nahant and 
Magnolia, Massachusetts; from Mount Desert Island, Cutler, several 
points in Penobscot Bay and several points in Casco Bay, Maine; 
after allowing for the effect on the basal layer of the manner of col- 
lecting, they agree very closely; specimens from Scotland and England 
agree equally well with Le Jolis’ plant. The writer formerly reported 
Р. cruenta as occurring in Southern Massachusetts;! a re-examination 
of the specimen shows that it is not a Petrocelis; so that as far as our 
records go, the genus is limited to the region north of Cape Cod. 
The marine flora of the New England coast from Cape Cod north 
is of a typical arctic character, but as is well known, there are excep- 
tional stations where plants characteristic of more southern regions 
occur; such stations have been recorded at Weymouth and Quincy, 
Massachusetts," Gloucester, Massachusetts,’ Penobscot Bay, Maine.* 
At all these stations there is much variation from one year to another, 
apparently on account of the difference in temperature, ete., in differ- 
ent years. An early spring, followed by a warm summer, will bring 
an abundant development of characteristic. southern forms, while 
1 Bull. Torrey Bot. Club, Vol. X, p. 56, 1883. 
2 Collins, Bull. Torrey Bot. Club, Vol. X, p. 29, 1884. 
3 Farlow, N. E. Marine Algae, p. 6, 1881. 
4 Qollins, Rhodora, Vol. I, p. 69, 1899. 
