1908] Collins,— Notes on Algae. IX 163 
ances in the Enteromorphas, which are most at home in ordinary sea 
water; in an increase in the Spirulinas, which are specially plants of 
lagoons and drying-up pools. Possibly these conditions may have 
induced the development of Gloeocystis scopulorum, mentioned earlier 
in this paper, from some Ulothrix which was here earlier in the season, 
but could not maintain its normal form under the summer conditions. 
One species remains to be mentioned; Chaetomorpha aerea (Dillw.) 
Kütz. This is usually spoken of as a common species on the New 
England coast, and if we include under the name the free-floating 
form known as C. Linum (Fl. Dan.) Kütz., just as what has been 
known as C. Picquotiana (Mont.) Kütz. is now considered a free form 
of C. Melagonium (Web. & Mohr) Kütz., this opinion is undoubtedly 
correct; the C. Linum form abounds from Long Island Sound to Passa- 
maquoddy Bay. But as to the attached plant, C. aerea in the older 
sense, the case is different. South of Cape Cod it is not uncommon 
and grows at low water mark and some distance above and below; but 
in 30 years collecting the writer has only twice found it north of Cape 
Cod, and in each case it was in a rock pool, at extreme high water 
mark; once at Cohasset, once at Marblehead, in both cases in small 
quantity. Here at the Ragged Island pools there was a dense growth 
around most of the edge, just below the water line; as densely packed 
as the grass in a lawn. ‘The filaments were all quite short, and there 
was a white band of dead fronds, above the water level, considerably 
broader than that of living fronds below the level; evidently the environ- 
ment had been exceptionally favorable to the species earlier in the 
season. In 1903 and 1906 nothing was seen of this species, and if 
we suppose that it is distinct from the floating C. Linum, it would be 
hard to account for its sudden appearance in such quantity; the cur- 
rents here tend southerly, and the chance of a frond or a spore being 
brought from southern New England and thrown up by the waves 
into the pool would be very small. Even if this were possible, there 
must have been several generations of plants in a very short time to 
produce this dense growth for such a distance. But if we suppose 
that it arose from the floating form, which is abundant in the vicinity, 
the spores finding favorable conditions, similar to those of warmer 
regions, all is clear. 
'To sum up as regards these two stations: 
conditions are subarctic, individual stations may be found where the 
conditions for a short time are almost subtropical; in such stations the 
even on shores where 
