208 Rhodora [AuGustr 
is *P. lignicola, crustacea, olivaceo-viridis, initio porosa, postea 
rimosa, mucosa : filis ramisque fasciculatis ; articulis diametro (41, — 
sls ^ = 0.00029 — 0.00038”) aequalibus vel duplo longioribus " ; 
and the fig. r11 is a reproduction of Kützing's in Tab. Phyc. 
In the Botanische Zeitung, Vol. XXXVII, p. 361, Pl. III, A, 1879, 
Reinsch describes and figures a new genus of the Chroolepideae, 
which he names Acrod/aste. ‘The plant grew on shells and pebbles 
in Buzzard's Bay, Massachusetts, and the description and figures are 
quite characteristic, but no name is given to the species. In Engler 
& Prantl, Die Natürlichen Pflanzenfamilien, i. abt. 2, p. 97, Wille 
recognizes the genus, and names the species A. Reinschii. In 
Notarisia, Vol. IV, p. 653, De Toni considers the two genera Pidinia 
and Acrod/aste as identical, and from the descriptions and the plates 
concludes that Reinsch's plant is merely the fruiting state of Z. 
rimosa. ln Syl. Alg., Vol. I, p. 259, 1889 he adds that this is 
confirmed by authentic specimens of Kützing's plant. Wille, how- 
ever, states, p. ror, that an investigation of authentic specimens of 
P. rimosa shows them to consist of young stages of various algae, 
especially Phycochromaceae, and he rejects the genus. 
In July, 1902, the writer was collecting algae at Harpswell, Maine, 
at the old tide-mill, mentioned in Ruopora, Vol. IV, p. 178, gathering 
especially Calothrix pulvinata (Mert.) Ag., which grows in extensive 
sheets on beams and posts under the mill. Dr. F. D. Lambert, of 
Tufts College, who was of the party, called attention to the fact that 
some of the coating on the timbers was of a yellowish green, quite 
distinct from the usual very dark, blackish green of the Calothrix. 
The writer supposed it must be due to exposure to the sun ; but when 
a specimen of the lighter colored material was examined, the next 
day, it proved to be quite a different plant, but agreed in every par- 
ticular with the description and plate of P. rimosa, and under this 
name it has been distributed as No. 971, Phycotheca Boreali- 
Americana. 
On a second visit to the place it was found that the P%/inia 
occupied a zone about half a meter in width, just below high water 
mark. Below this it passes into the Ca/o¢hrix, the “neutral ground ” 
occupying about half a meter, through which distance the Calothrix 
increases from a very slight admixture and the Piinia diminishes 
correspondingly. Below this neutral ground there is no ZY/aa. 
The color changes gradually, from the rather light yellowish green 
