1924] Lewis,—The Flora of Penikese 189 
been brought ky currents, two are adapted to dispersal by animals, 
and one (Quercus) does not belong in any of these categories. 
It seems likely that man is the most efficient agent for the intro- 
duction of new species, birds second, and wind third, while other 
agencies are relatively unimportant. 
MARINE ALGAE. 
As might be expected, the marine algae of Penikese differ with 
differing location and exposure. On the rocky northwest shore, 
where deep water comes close to the land, the dominant species are 
the larger tougher Phaeophyceae, such as Ascophyllum, Fucus, 
Laminaria, Chordaria, and Dictyosiphon, with some Ectocarpus and 
Elachistea. The only common green alga is Cladophora, while the 
Florideae are represented especially by Cystoclonium and Corallina. 
Noticeably absent are the Polysiphonias, Ceramiums, Mesogloia, 
and other feathery species which are very abundant in the region 
generally. 
In the bay on the southwest shore there is distinctly less of the 
rockweeds, while Polysiphonia fastigiata is abundant, with much small 
Leathesia. Dictyosiphon is also common here, as are Ralfsia and 
Corallina. 
'The southern end of Tub Point was explored carefully as being 
representative of the type of shore seen all around the island except 
to the eastward. The rocky shore runs out southward to several 
large boulders exposed at low water. Here are Fucus and Ascophyllum 
in abundance, with Calothrix forming a dense turf on them, and 
much Cladophora on the boulders. On the rocks nearer the shore 
Ralfsia, Hildenbrandtia, Lithothamnion, and Protoderma are common. 
On the Fucus are found Chondria, Polysiphonia, Ceramium, Leathesia, 
and Elachistea. A little deeper occur Mesogloia, Chordaria, and 
Dictyosiphon. At a depth of three feet or so are found Chorda, 
Laminaria Agardhii and L. digitata, Scytosiphon, Punctaria, and 
Corallina. In the deeper water, from four to six feet, the common 
forms are Phyllophora, Chondrus, Ahnfeltia, and Laminaria Platy- 
meris. 
The eastern side of the island is fringed with eel grass, with fairly 
shoal water extending out some distance. Here the algal flora is 
relatively sparse, and quite different from that characteristic of the 
more exposed and rocky shores. The representative forms here are 
