BIOLOGICAL SURVEY OF WOODS HOLE AND VICINITY. 449 



water are colored, not the characteristic red of this group, but shades of brown and 

 green; for example, the Irish moss, Chondrus crispus, is frequently green under bright 

 illumination in the summer at Woods Hole. Furthermore, Nadson (1900) has shown 

 that certain species of the Cyanophyceae and Chlorophyceae, which are green near the 

 surface, take on reddish colors in deep water. 



These conclusions that the colors of algae depend upon the quality of the light are 

 opposed to views held by Berthold (1882), Oltmanns (1892), and others who have con- 

 sidered the Rhodophyceae to be merely shade plants, the distribution of which was deter- 

 mined by the quantity of light. They have made much of the fact that in dimly lighted 

 caves and shaded situations red algae, which usually grow at some depth, are found very 

 near the surface; but it should be borne in mind, as Borgesen (1905, pp. 702, 703) points 

 out, that while these algae receive a much weaker white light in these caves, they may 

 have the benefit of much blue and green reflected light. 



Gaidukov (1902, 1906), in a series of interesting experiments, has shown that certain 

 algae (species of Oscillatoria, Phormidium, and Porphyra) take on complementary colors 

 when subjected to pure rays from a spectrum, becoming, for example, green under red 

 and yellow light and red or purplish under green or blue light. This phenomenon, called 

 complementary chromatic adaptation, is shown only by living plants and is believed to 

 involve changes in the structure of the pigments. The reason why green algae can not 

 live in deep water is clear, since the red rays upon which they depend are not there 

 present. The red algae, on the contrary, may live at the surface as well as at depths 

 below the penetration of red rays, but at the surface they meet the competition with 

 green algae from which they are free in deep water. 



However, it can not be said that all of the phenomena are clearly explained by the 

 hypothesis of chromatic adaptation held by Engelmann and Gaidukov. Thus, Rodriguez 

 (1888) reports the following Chlorophyceae off the Balearic Islands at much greater depths 

 than would be expected for any of the green algae: Palmophyllum orbicularis Thuret, 

 130 meters; Cladophora pellucida Kutzing, 40 meters; Codium tomentosum Agardh, 48 

 meters; C. tomentosum var. elongatum, 90 to 100 meters; Udotea Desfontainii Decaisne, 120 

 meters ; and somewhat similar records are known for certain of the Chlorophyceae in the 

 Gulf of Naples. 



7. TEMPERATURE AND SEASONAL CHANGES. 



The temperature of the water, the depth, and the character of the bottom are the 

 chief factors in determining the distribution of the algae in the region covered by the 

 survey. The influence of temperature must be of fundamental importance where the 

 seasonal extremes are as great as those of the summer and winter at Woods Hole. The 

 conditions in the winter would admit a rich northern or boreal algal flora at Woods 

 Hole were it possible for the species to reach this sheltered situation by traveling around 

 Cape Cod and to survive the warm summer. As it is, a number of northern species do 

 grow at Woods Hole in the favorable winter and spring seasons and some are able to 

 vegetate through the summer. In striking contrast with the winter's cold is the summer 

 temperature, which is so high that it can support a flora with many points of resem- 

 blance to the floras of warmer seas. The subject of temperature receives considerable 

 attention in section 1, chapter n, pages 38-52, where the detailed records of the Survey 

 16269 — Bull. 31, pt 1 — 13 29 



