448 BULLETIN OF THE BUREAU OF FISHERIES. 



at the deepest stations have shown abundant growths of algae wherever the bottom was 

 suitable, but two of the deepest stations in the westerly portion of Vineyard Sound (7682 

 and 7683, 19 and ig}4 fathoms, respectively) were over a sandy bottom unfavorable for 

 the attachment of algae. Station 7670 (19 fathoms), in Buzzards Bay west of the island 

 of Penikese, showed a stony bottom with many plants of Laminaria Agardhii var. vittata, 

 and in small quantity Champia parvula, Chondrus crispus, Ceramium rubrum, Grinnellia 

 americana, Polysiphonia urceolata, and Rhodymenia palmata. 



6. LIGHT. 



As stated above, the depth to which certain algae 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 Cyanophycese, or blue green algae, and the Chlorophyceae, or green algae, 

 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 Rhodophyceae, or red algae, reach the lowest depths, although 

 many species grow near low-water mark and some even above it. The Phseophyceae, 

 or brown algae, are somewhat midway between the green and the red algae in their light 

 relations. Some species of the brown algae 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 algae. There are apparently no regions in Buzzards Bay 

 and Vineyard Sound too deep for certain species of brown algae, for Desmarestia aculeata, 

 Laminaria Agardhii, and Laminaria Agardhii var. vittata were found between 17 and 

 19 fathoms. The list of red algse 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 Brodicei, Phyllophora 

 membranifolia, Plumaria elegans, Polysiphonia elongata, Polysiphonia urceolata, Rhody- 

 menia palmata, Spermothamnion Turneri. 



There is therefore in a broad sense a distribution of algae in zones depending upon 

 light relations, the blue-green and green algae growing under the brightest illumination, 

 the brown algae requiring on the whole less light, and the red algae 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 

 algae growing side by side and even with the green alg8e under very bright illumination. 



It is a matter of dispute whether the life habits of marine algae 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 algae. According to this view 

 the green algae grow under bright illumination because they require the maximum of 

 red rays, while the red algae are able to live in deep water because their color allows 

 them to absorb the green rays which they especially need. The brown algae in 

 general adjust themselves to light conditions intermediate between these extremes. It 

 is well known that a number of the Rhodophyceae which grow near the surface of the 



