2 THE VOYAGE OF H.M.S. CHALLENGER. 



further of innumerable kinds of sea-weed as growing upon the rocks. Mr McCormick, in Ross's 

 Antarctic Voyage, speaks of a conferva of which the sea-birds build their nests. Sir Joseph Hooker, 

 in his Flora Antarctica, refers to Darwin's admirable account of the island. 



" I spent about twenty-four hours on the rocks during our two days' stay, and searched carefully 

 for botanical specimens. The sea-weeds, instead of being present in innumerable kinds, are, as far 

 as I could ascertain, comparatively few in number, very few species apparently being able to hold 

 their own in the constant heavy surf. 



" About tide-mark, and indeed forming the mark, there is, as at St Vincent, a band of dense 

 pinkish-white incrustation, consisting of a calcareous alga, which is bored in all directions by a small 

 tubicolous annelid. This is evidently the reddish band referred to by Mr McCormick as the work 

 of coral insects. In some places the incrustation is white, with a different surface, and probably 

 consisting of a different species of alga. 1 Above the line of incrustation the rocks are covered for 

 several feet with a dark red stain, consisting of an alga 2 of which specimens were preserved in fluid ; 

 and here, where the rock is alternately covered and left bare by the surf, grows a short filamentous 

 alga, which has tufts of a green conferva adhering to it. The rocky bottom in the small, 

 comparatively sheltered bay formed by the circlet of rocks is covered with a dense growth of a green 

 alga, which extends out a short distance beyond the mouth of the bay to the depth of twenty 

 fathoms (whence I got up specimens on a fishing-line), and also grows abundantly on the exposed 

 side of the island, as I saw on looking down into the water from the summit of the highest peak. 

 The alga (Caulcrpa clavifera) is constantly loosened by the surf from the bottom, and, floating to the 

 surface, is gathered by the noddies (Sterna stolida) to build their nests ; the boobies (Sula fused) 

 apparently do not use it. A second smaller but similar species grows with this alga in the bay. 

 I found only one or two other alga;, and when looking down into the water from above could see 

 only the larger green species covering the bottom. The water deepens so very rapidly around the 

 rock that it is improbable that many species of alga; grow on it ; in fact, the marine flora seems to 

 be remarkably poor. 



" On the aerial surface of the rock I found a green Chlorococcus growing in sheltered crevices, 

 on concretionary masses formed of guano mixed with the pupa) of the pupiparous fly Olfcrsia, 

 discovered by Darwin on the island, and spiders' webs. The Chlorococcus is the only aerial plant on 

 the island, and it is not abundant. In some pools of stagnant water are some few diatoms and 

 Oscillatoricc. In some places there are a few bushels of guano to bo found in hollows in the rock. 

 I boiled some of this with nitric acid ; it was almost wholly soluble, and I could find no diatoms in 

 the small residue.' Peruvian guano contains abundance of diatoms. A Coscinodiscus has occurred 

 sparingly of late upon the surface of the sea; and it might have been expected to find its way 

 through (he small surface-animals into the fish and thus into the guano. Diatoms have as yet, 

 however, never been abundant either at the surface or on the sea bottom. In the curious veins of 

 conglomerate which traverse the rock in all directions, and are described by Darwin and Mr 

 McCiinnick, arr l'- il fragments of nulHporic incrustation mingled with pebbles ami broken Bhells." 

 — //. X. Moseley. 



Altogether only seventeen species of vegetable organisms Lave been collected on and in 

 the vicinity of the Rocks, and they are all algae. 



1 Lithothamnion polymorjphum. 2 llildcnbrandtia expunsa. 



