240 CORALLINES. PART n, 



the midrib. 5 The Delesseria sanguinea is now known 

 as the Wormskioldia sanguinea. 



The Corallines are florid Algse, which absorb such a 

 quantity of carbonate of lime from the surrounding 

 water, that they become rigid, hard, and often stony. 

 They are purple or pink when fresh, white and some- 

 times brittle when dry, and are propagated by strings of 

 spore threads rising from the base of the nuclei which are 

 enclosed in conceptacles or spore cases, open at the top. 

 Some are articulate, composed of closely compacted 

 threads, as the Corallina omcinalis, a pretty little 

 branched and bushy plant, most luxuriant in deep water, 

 and particularly abundant in the rocky pools. Its 

 urn-shaped spore sacs are attached to the tips or sides 

 of the branches ; fig. 24 c is a vertical section of one 

 of them magnified, and d is a membrane of the same, 

 more highly magnified, with impressions of the exter- 

 nal cells. The joints of the articulate corallines, which 

 are flexible and vary much in length, are either free 

 from carbonate of lime, or ornamented with calcareous 

 plates ; it is through these open spaces that the plant is 

 believed to obtain nourishment. The forms of the co- 

 rallines are varied beyond description ; many are mere 

 amorphous crusts on stones and sea weeds, increasing 

 from the centre outwards as in the lichens, others are 

 lobed and branched like real corals. Corallines ascend 

 to very high latitudes, but abound most in warm and 

 tropical seas : either free, or coating pebbles at vast 

 depths, they form the last zone of vegetable life. 



The Laurenciacese have fronds which are soft and 

 thread-like, or solid, fleshy, and inarticulate ; both are 

 repeatedly branched. The colour of these plants is 

 purple or a dullish red, but they are extremely sensitive 

 to the influence of light and air, changing through 

 every shade of orange, yellow, or green, according to the 



* Mr. Berkeley's ' Cryptogamic Botany.' 



