GROUP I. THALLOPHYTA : ALG^ : EHODOPHYCE^E. 267 



Sargassum), or dioecious (e.g. Himanthalia, Ascophyllum, Fucus vesiculosus and 

 serratus) ; in the former case each conceptacle contains both antheridia and 

 oogonia. 



The oospore, which is the product of the fertilisation of an oosphere, germin- 

 ates without any period of quiescence. It first becomes somewhat pear-shaped ; 

 it is then divided into two by a transverse wall ; the more pointed of the two 

 cells forms the primary root, whilst the other gives rise to the shoot (Fig 190 d.) 



Sub-Class IV. RHODOPHYCEJ] or Red Algae. Multicellular 

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

 sometimes differentiated into stem and leaf ; flattened or fila- 

 mentous ; when filamentous, consisting of a single longitudinal 

 row of cells (monosiphonous) or of several rows (polysiphonous} 

 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 alternately right 

 and left ; the flattened forms grow by means of a marginal series 

 of initial cells ; but in the Bangiaceae there is no growing-point, 

 all the cells being merismatic : branching, generally monopodial, 

 but sometimes sympodial (e.g. Plocamium, Dasya) : adventitious 

 roots common. 



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

 is rare. 



Reproduction by means of asexually produced spores occurs 

 throughout the sub-class ; the sporophyte (cystocarp) always 

 produces spores (carpospores) ; the gametophyte usually produces 

 gonidia (usually tetragonidia) except in the Lemaneacea3 and most 

 Helminthocladiaceae ; the gonidia are, as a rule, not borne on indi- 

 viduals which produce sexual organs (actual gametophytes), but 

 on distinct individuals (potential gametophytes), though there are 

 exceptions to this rule (e.g. Lomentaria kaliformis, Callithamnion 

 corymbosum, Polysiphonia variegata, etc.). 



The gonidia are produced in unilocular gonidangia, either 

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

 commonly in fours ; hence they are generally termed tetragonidia. 

 The tetragonidia may be formed tetrahedrally in the gonidangium ; 

 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 gonidangia on the shoot is various. In 

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

 cells of short lateral branches become gonidangia. In forms of 



