SIPTIONACEiE. 
15 
But there is found in Caulerpa a supplementary structure of a very peculiar and curious 
kind, which has induced several systematic writers to separate this genus, as the type 
of a family distinct from the other Siphonese. 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, wfiich 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 plant, intended to give strength and unity to all parts 
of the frond. The filaments appear to be tubular, 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 35° 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. clavifera 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. clavifera , 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. lycopodium , 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 Bed Sea, but appears to be essentially characterised by its 
woolly stems. The Bed 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. 
