ALGAE — MEIER 413 



rocks following the course of running water. A small alga gives 

 the granite rocks at Rio de Janeiro, Brazil, their brown color, and 

 a blue-green alga colors the lime walls of the precipices of the Rhae- 

 tikon Mountains in Austria, a bright blue color. On the Tsclimanin- 

 Tal of the Tyrol in Austria, from 1,000 to 2,500 meters above sea 

 level on the west to the southeast sides, the effect of the light in- 

 tensity governs the appearance of the algae. On the outside of the 

 cliffs nearest the light are the felty masses of yellow and brown 

 Scytonema and blue Gloeoca'psa, while on the inside of the cliffs 

 away from the light the Gloeocapsa mats are colorless. On the up- 

 per surfaces of stones may appear a bright orange wealth of Tren- 

 tepohlia, while on the lower surface are colorless plants of Gloeo- 

 ca^psa. When a chemical analysis was made of the food material 

 obtainable in these rocks for the algae, it was found to be as fol- 

 lows: Calcium oxide, 30.67 percent; magnesium oxide, 21.49 percent; 

 carbon dioxide, 47.2 percent; ferric oxide, 0.22 percent; and man- 

 ganese oxide, 0.28 percent. 



On the inland cliffs of Natal, in Africa, the earliest and perhaps 

 the only possible colonist was the blue-green alga Gloeocapsa san- 

 guinea. On the rocks dripping with moisture is also found Stigo- 

 nema^ whose yellow, brown, and black threads are almost completely 

 enshrouded with the red coiling filaments of Schisothrix. Other- 

 wise, the cliffs are covered with black lithophilous Cyanophyceae. 

 In dry weather these algae shrivel and peel off, thus restoring the 

 original color of the cliffs. The algae have to withstand adverse 

 conditions of drought and cold only during a comparatively short 

 period on these cliffs, conditions that are not so extreme on the 

 Drakensburg Cliffs as in the lower dry river valleys. 



A beautiful example of the zonation of algae on cliffs exists on 

 the islands of South Orkney, Ireland. At Green Head the face of 

 the cliffs that look out toward the wrecks of the sunken German 

 fleet is marked with great streaks of color as if by a gigantic paint- 

 brush. Lower seaward, where the waves pound against the shore 

 when the sea is rough, the colors appear in big patches. At the 

 top of the cliff is a black mourning frame of Verrucaria maura 

 about 2 feet in depth, then below that in the following order: A 

 yellowish green stripe about a foot deep of Pelvetia, a 3-foot band 

 of orange-green Fucus spiralis^ long straplike fronds of olive-yellow 

 Ascophyllum nodosum and Polysiphonia fastigiata extending for 3 

 feet in depth, dull green patches of Fucus vesiculosis, and Fucus 

 serratus^ distinctly green in the light though dark in the shade, 

 spreads itself out over the flat stones near the low-water mark. 

 Truly this is a colorful monument that nature has raised. 



