SIPHONACE.E. 15 



But there is fouud in Caulerpa a supplementary structure of a very peculiar and curious 

 kind, which has induced several systematic \vi-iters to separate this genus, as the type 

 of a fomily distinct from the other Siphoneaj. An unwillingness needlessly to multiply 

 families, and a belief that synthesis, much more than analysis, ought to be the study 

 of a system framer, has prevented my adopting these views. The structure alluded to 

 is this : from the inner face of the wall of the membrane covering the frond there issue 

 innumerable, cylindrical, filamentous processes, which seem to be merely internal ex- 

 tensions of the cell walls, and not new cells. These branch and anastomose together 

 into a kind of spongy net-work that fills the whole cavity of the frond, and is bathed 

 and its fibres keep apart by the grumous fluid. This spongy net-work may be regarded 

 as the proper frame-work of the i)lant, intended to give strength and unity to all parts 

 of the frond. The filaments appear to be tulndar, but are empty and colourless. This 

 peculiar modification of structure is so like that of a sponge, that we may almost regard 

 a Caulerpa as a vegetable sponge enclosed in a membranous epidermis. 



The genus Caulerpa is eminently characteristic of the tropical and subtropical oceans 

 and seas of both hemispheres. Very few species extend far into the temperate zone. 

 The most northern are found in the Mediterranean Sea ; and the most southern on the 

 shores of New Zealand. Many species exist on the southern coast of Australia, in 

 lat. 35° or 36° ; but the greater number are found within 3.5° of the equator. They 

 inhabit the littoral zone, from near high-water to low-water marks ; and some extend 

 into the laminarian zone, or even to that of the Nullipores. Their favorite locality is 

 on hard sand, or on sand-covered rocks ; and in the crevices of coral on the coral reefs, 

 and more particularly in hollows left on the surface of the reef, where the corals have 

 ceased to grow. Most of the American species grow within tide marks, but are not 

 luxuriant except at low-water mark, or a little below it. C davifera commences to 

 grow nearly at high water mark, and is continued throughout the whole littoral zone 

 and into the laminarian. It consequently varies greatly in size and in general aspect, 

 and accordingly appears under several names in botanical works ; but these " book- 

 species," however distinct they may look in the herbarium, cannot be recognized on 

 the shore, where all the forms gradually blend together. Some of the species are very 

 local. Others are found in both hemispheres, and in the Atlantic and Pacific Oceans. 

 Of the North American species C plumaris, C davifera, C. ericifolia and C cupressoides 

 are the most widely dispersed, being found in all tropical waters ; C prolifera is found 

 in the Mediterranean Sea ; C. paspaloides on the coast of Brazil, while C Ashmeadii 

 and C. lycopodiam, so far as is yet known, are peculiar to the Keys of Florida. C. 

 mexicana very closely resembles C. asplenioides, Grev. a native of the Indian Sea, and 

 it is questionable whether these are distinct ; and C. lycopodium also is nearly allied 

 to C. selago, a native of the Eed Sea, but appears to be essentially characterised by its 

 woolly stems. The Pted Sea, the Persian Gulf, the shores of tropical Asia and those of 

 New Holland, with the coral reefs of the Pacific furnish many local species, some ex- 

 ceedingly curious and beautiful. Several species are eaten by the natives of the 

 Pacific archipelagoes ; and all furnish a favourite food to the turtle, whose green fat 

 they serve to nourish. 



