GROUP I. THALLOPHYTA : ALG.E. 271 



Sub-Class IV. RHODOPHYCE.E (FLORIDELE) or Red Algae. Multi- 

 cellular plants ; body, generally differentiated into shoot and root ; 

 shoot, sometimes differentiated into stem and leaf ; flattened or 

 filamentous ; when filamentous, consisting of a single longitu- 

 dinal row of cells (monosiphonous} or of several rows (polysi- 

 phonous") with or without a small-celled cortex , the filamentous 

 forms grow by means of a single apical cell from which segments 

 are cut off either by transverse walls, or by oblique walls alter- 

 nately right and left ; the flattened forms grow by means of a 

 marginal series of initial cells ; but in the Bangiacese there is 

 no growing-point, all the cells being merismatic : branching, 

 generally monopodial, but sometimes sympodial (eg. Plocamium, 

 Dasya) ; adventitious roots common. 



Vegetative reproduction by gemmae (e.g. Monospora, Melobesia) 

 is rare. 



The plant, as a rule, produces tetrasporcs asexually, but they are 

 usually not borne on individuals which produce sexual organs, 

 but on distinct individuals, though there are exceptions to this 

 rule (e.g. Lomentaria kaliformis, Callithamnion corymbosum, 

 Polysiphonia variegata, etc.). 



The spores are produced in unilocular sporangia, either singly, 

 or two together, or sometimes as many as eight, but most commonly 

 in fours; hence they are generally termed tctraspores. They 

 may be formed t etrahedrally ; or by transverse divisions, when 

 they are said to be zonate ; or by two divisions at right angles 

 to each other, when they are said to be cruciate. 



The arrangement of the sporangia on the shoot is various. In 

 simple monosiphonous forms (e.g. Callithamnion) the terminal 

 cells of short lateral branches become sporangia. In forms of 

 more complex structure the sporangia are developed internally, 

 within the superficial layer of tissue. The sporangia may be 

 scattered over the surface of the shoot, or collected into special 

 receptacles of various forms. In some cases (e.g. some Rhodome- 

 lacese, such as Polysiphonia) the sporangia are confined to certain 

 specially modified branches which are termed sticliidia. The tetra- 

 sporas are set free as spherical unciliated cells without a cell- wall. 



The sexual organs are antheridia and procarps ; they are usually 

 borne by distinct individuals, but in some cases on the same (e.g. 

 Grateloupia, Halymenia, Halarachnion, Xemastoma, Dudresnaya 

 ciccinea &n& purpurifcra, Glceosiplionia capillaris, ITelminthora 

 dicaricata}. 



