STPHONACE^. 11 



lower half, which retains its union with the branch : and now the change is complete. 

 The anther thus formed consists of an isolated, curved, cylindrical, nearly colourless but 

 not empty cell, supported on a pedicle of variable length and curvature. In the anther- 

 cell spermatozoids are gradually evolved out of the contained matter, and are at maturity 

 emitted through an opening at the summit of the cell. So much for the structure of 

 the anther. The sporangium, or female organ, is placed on the branch close to the antheri- 

 dium, and like it, at first consists of a papilla, or minute ramulus rising from the branch. 

 It does not, however, lengthen into a cylinder, but assumes an ovoid form ; its contents 

 become dense and granular ; a diaphragm separating it from the branch is formed across 

 its base, and thus it becomes a separate egg-shaped cellule, sessile on the branch from 

 which it has been formed. A beak-like attenuation, directed toward the adjacent 

 antheridium, is now formed, and becomes at length perforated. At the same time the 

 antheridium, having curled round, directs its extremity toward the sporangium ; its 

 summit opens, aud the enclosed spermatozoids are discharged into the water, close to 

 the orifice of the sporangium, which they enter and efiect the fertilization of the matter 

 aggregated within. A cell-wall is then formed round the fertilized substance, which 

 thus becomes a spore, which gradually ripens and is detached on the bursting or decay 

 of the membranous cyst within which it was formed. In its process toward ripening 

 it loses its green colour, and at length becomes nearly colourless, except for one or more 

 brown masses which it contains. In this state it remains, often for a considerable time, 

 till germination takes place, when it suddenly resumes its green, and then elongates 

 into a tubular cell, which assumes the form and ramification of the parent plant. 



This Order is dispersed, under one or other of its forms, over most parts of the world, 

 and its species are found either in the sea, in fresh water, or occasionally on damp soil ; 

 some species of Vaucheria and the curious little Botrydium being terrestrial. The 

 geographical range of several species is very extensive. Codium tomentosum and 

 Bryopsis plumosa are common to the Northern and Southern Oceans and to the 

 Eastern and Western Hemispheres, and are both found in the warmest parts of the 

 tropical seas, as well as in high latitudes of the temperate zones. Caulerpa is specially 

 characteristic of the tropical ocean, where its species are numerous, some of the more 

 common kinds forming the principal algoid covering of rocks or sands in shallow wat«r. 

 Some of its species are widely scattered, and others apparently limited to a few spots. 

 Several of the fossil algoid plants appear to have been Caulerpce, and the fossil figured 

 by Brongniart (tab. 9, bis, fig. Ij, under the name " Fucoides hypnoides," bears a very 

 striking resemblance to Caulerpa hypnoides of the Australian coast. 



SYNOPSIS OF THE NORTH AMERICAN GENERA. 



Sub-order I. CaulerpEjE. Frond with prostrate, rooting, primary stems (surculi), and 

 erect branches, membranous, unicellular ; cell within filled with a network of 

 branching fibrils. 



I. Caulerpa. 



