448 BULLETIN OF THE BUREAU OF FISHERIES. 
at the deepest stations have shown abundant growths of alge wherever the bottom was 
suitable, but two of the deepest stations in the westerly portion of Vineyard Sound (7682 
and 7683, 19 and 19!4 fathoms, respectively) were over a sandy bottom unfavorable for 
the attachment of alge. Station 7670 (19 fathoms), in Buzzards Bay west of the island 
of Penikese, showed a stony bottom with many plants of Laminaria Agardhw var. vittata, 
and in small quantity Champia parvula, Chondrus crispus, Ceramium rubrum, Grinnellia 
americana, Polysiphonia urceolata, and Rhodymema palmata. 
@., LIGHT. 
As stated above, the depth to which certain alge may descend depends upon the 
penetration of light. The factor that determines the lowest limits of algal life is not 
depth of water but absence of light. 
The Cyanophycee, or blue green alge, and the Chlorophycee, or green alge, 
require the greatest illumination and are rarely, if ever, found at Woods Hole and vicinity 
in water more than 2 or 3 fathoms deep, but are for the most part near the surface or 
between tide marks. The Rhodophycee, or red alge, reach the lowest depths, although 
many species grow near low-water mark and some even above it. The Phzophycee, 
or brown alge, are somewhat midway between the green and the red alge in their light 
relations. Some species of the brown alge grow at low-water mark and above, but 
many grow below low water and to a considerable depth; few, however, are found at 
the greater depths of the red alge. There are apparently no regions in Buzzards Bay 
and Vineyard Sound too deep for certain species of brown alge, for Desmarestia aculeata, 
Laminaria Agardhii, and Laminaria Agardhu var. vittata were found between 17 and 
19 fathoms. ‘The list of red alge present at these depths (17 to 19 fathoms) is, how- 
ever, much longer: Champia parvula, Chondrus crispus, Cystoclonium purpurascens var. 
cirrhosum, Delesseria sinuosa, Grinnellia americana, Phyllophora Brodiei, Phyllophora 
membranijolia, Plumaria elegans, Polysiphonia elongata, Polysiphoma urceolata, Rhody- 
menia palmata, Spermothamnion Turnert. 
There is therefore in a broad sense a distribution of alge in zones depending upon 
light relations, the blue-green and green alge growing under the brightest illumination, 
the brown alge requiring on the whole less light, and the red algz able to flourish under 
the weakest illumination. It must constantly be borne in mind, however, that there is 
always an overlapping in the habitat of species among these groups, many brown and red 
alge growing side by side and even with the green alge under very bright illumination. 
It is a matter of dispute whether the life habits of marine algze with respect to illu- 
mination are influenced chiefly by the quality of the light or by the quantity. The red 
rays of sunlight, it is claimed, can not penetrate much below 7 fathoms, and the light 
at greater depths is mainly composed of blue and green rays, is feeble in yellow, and 
lacks red rays entirely. Certain investigators, notably Engelmann (1883, 1884) and 
Gaidukov (1902, 1904, 1906), hold that the quality of the light rather than its intensity 
determines the distribution of the green, brown, and red alge. According to this view 
the green alge grow under bright illumination because they require the maximum of 
red rays, while the red alge are able to live in deep water because their color allows 
them to absorb the green rays which they especially need. The brown alge in 
general adjust themselves to light conditions intermediate between these extremes. It 
is well known that a number of the Rhodophyceze which grow near the surface of the 
