78 FLORIDE^E. 



The carpospores are destitute of cell- wall and arise directly by 

 the division of the fertilised oosphere. The Bangioidege occur 

 chiefly in salt water. 



Order 1. Goniotrichaceae. The thallus consists of a branched cell- 

 filament without rhizoids. Tetraspores are formed directly from the entire 

 contents of the mother-cell, without any preceding division. Fertilisation 

 unknown. Asterocystis, Goniotrichum. 



The Goniotrichacece, through the blue-green Asterocystis, are allied to the 

 Myxophyceffi, and through Goniotrichum to the Porphyracece. 



Order 2. Porphyraceae. The thallus is formed of an expansion consisting 

 of a layer of 1-2 cells, which, at the base, are attached to the substratum by 

 means of a special form of haptera (Porphyra, Diploderma) ; or of unbranched 

 (very rarely slightly branched) filaments, attached at the base by haptera 

 (Bangia) : or it extends from a prostrate cell-disc (various species of Frytliro- 

 trichia). Tetraspores are formed after one or more divisions of the mother-cell, 

 either from the whole or only a part of its contents ; they possess amoeboid 

 movements, or have a jerky, sliding-forward motion. The antheridia have 

 the same appearance as the vegetative cells, but divide several times, and 

 several spermatia are formed, either simultaneously from the whole contents 

 (Porphyra, Bangia), or the spermatia are successively formed from a part of 

 the contents of the antheridium (Erythrotrichia). The carpogonium is with- 

 out a trichogyne, but the oosphere has a colourless spot which may some- 

 times rise a little above the surface of the thallus, and may be considered 

 as an early stage in the development of the trichogyne. The spermatia form 

 a canal through the membrane of the carpogonium, and their contents coal- 

 esce with the oosphere at its colourless spot. The fertilised oosphere divides 

 on germination into a number of carpospores, which are set free as naked, 

 motionless masses of protoplasm, which grow and give rise to new individuals 

 (alternation of generations). 



Family 2. Florideae. 



The thallus has one or more apical cells, grows principally by 

 apical growth, and may be differentiated into root, stem, and leaf. 

 The chromatophores vary in form, but have a red or brownish 

 colour, due to chlorophyll and phycoerythrin. Asexual repro- 

 duction by motionless tetraspores, which generally arise by the 

 division into four of the contents of the tetrasporangium. The 

 carpogonium has a trichogyne, and the carpospores, which are 

 formed indirectly from the fertilised oosphere, possess a cell- 

 wall. 



The thallus may assume very different forms. In the simplest 

 species it is filamentous and formed of single, branched rows of 

 cells (Callithamnion, etc., Fig. 73). Ceramium has a filamentous, 

 thallus. generally dichotomously forked (Fig. 75), or sometimes 



