98 TENTH ANNUAL REPORT OP 



that level, and a few straggle into deeper water, sometimes into very 

 deep water. The gigantic deep-water Algas, 3Iacrocystis , Nereocys- 

 tis, Lessonia, and Diirvillcea, are olive-colored. 



i?e(i-colored AlgfB are most abundant in the deeper and darker 

 parts of the sea, rarely growing in tide pools, except where they are 

 shaded from the direct beams of the sun either by a projecting rock, 

 or by over-lying olivaceous AlgtB. The red color is always purest 

 and most intense when the plant grows in deep water, as may be seen 

 by tracing any particular species from the greatest to the least depth 

 at which it is found. Thus, the common Ceramium ruhrum in deep 

 pools or near low-water mark is of a deep, full red, its cells abun- 

 dantly filled with bright carmine endochromCj which will be dis- 

 charged in fresh water so as to form a rose-colored infusion ; but the 

 same plant, growing in open, shallow pools, near high-water mark, 

 where it is exposed to the sun, becomes very pale, the color fading 

 through all shades of pink down to dull orange or straw-color. It 

 is observable that this plant, which is properly one of the red series 

 (or Rhodosperms,) does not become grass-green (or like a Chlorosperm) 

 by being developed in the shallower water, but merely loses its capa- 

 city for forming the red-colored matter peculiar to itself So, also, 

 Laurencia pinnatifida, and other species of that genus, which are nor- 

 mally darkpurjile, are so only when they grow near low-water mark. 

 And as many of them extend into shallower parts, and some even 

 nearly to high-water limit, we find specimens of these plants of every 

 shade of color from dull purple to dilute yellow or dirty white. 

 Similar changes of color, and from a similar cause, are seen in Chon- 

 drus crispus, the Carrigeen or Irish Moss, which is properly of a fine 

 deep purplish red, but becomes greenish or whitish when growing in 

 shallow pools. The lohite color, therefore, which is preferred in car- 

 rigeen by the purchaser of the prepared article, is entirely due to 

 bleaching and repeated rinsing in fresh water. 



Many Alga?, both of the olive and red series, and in a less perfect 

 manner a few of the grass-green also, reflect prismatic colors when 

 growing under water. In some species of Cystoseira, particularly in 

 the European C. ericoides and its allies,, these colors are so vivid that 

 the dull olive-brown branches appear, as they wave to and fro in the 

 water, to be clothed with the richest metallic greens and blues, 

 changing with every movement, as the beams of light fall in new di- 

 rections on them. Similar colors, but in a less degree, are seen on 

 Ghondrus crispus when growing in deep water ; but here the prismatic 

 coloring is often confined to the mere tips of the brandies, which 

 glitter like sapphires or emeralds among the dark purple leaves. The 

 cause of these changeable colors has not been particularly sought 

 after. The surface may be finely striated, but it does not seem to be 

 more so than in other allied species, where no such iridescence has 

 been observed. In the Chondrus the changeable tints appear to 

 characterize those specimens only which grow in deep water, and 

 which are stronger and more cartilaginous than those which grow in 

 shallow pools. 



Fresh water has generally a very strong action on the colors as 

 well as on the substance of marine Algas which are plunged into it. 



