RHODOSPERMEA. 12] 
to the fronds of several of the membranous algz. Most of these latter 
species belong to the sub-crder Nulliporew, some of which vegetate only 
in deep water, and are thus unobtainable except by dredging. The 
plants of this Order are found in all seas, but are most abundant in warm 
climates, and some of the tropical species are among the most beautiful 
and curious of the oceanic flora. Many of these plants were formerly 
regarded as of an animal rather than of a vegetable nature, and until 
lately they were classed among the zoophytes or polyp-bearing corals. 
They are, however, now known to be true vegetables ; for upon the plants 
Fig. 111. Coralluna officinalis. 
being immersed in strong acid, the limy coating of their fronds is 
dissolved, and the vegetable structure is at once revealed. The fructi- 
fication in this Order is tetrasporic, but, curiously enough, is, for the most 
part, contaized in conceptacles which are very similar in form to those 
which, in other genera, contain spores. This assemblage of plants consists 
of two distinctly marked sub-orders. ‘The first of these, called Coral- 
linee, contains the branched and jointed species. Fig. 111, represents a 
branch of the well-known Corallina officinulis, the most abundant of th 
M 
