CRYPTOGAMS 



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Fig. 260. — Gigartina mamniillosa. s, Wart-sliaj)ed 

 cystocarps. (| nat. size. Officinal.) 



Gif/artina mamniillosa, Fig. 260) ; while in still other species it consists 

 of expanded cell surfaces attached to a substratum. 



The forms with more advanced segmentation resemble the vascular 

 plants externally, and exhibit a 

 differentiation into a cylindrical 

 axis and flattened leaf-like thalloid 

 branches which, as in Delesseria 

 (Hydrolaputhum) sanguined, may 

 even be provided with middle and 

 lateral ribs (Fig. 9, p. 13). All 

 the Florideae are attached at the 

 base by means of rhizoidal fila- 

 ments or discoid hold-fasts. In 

 the more delicate species the cell 

 walls are thin ; while in the firmer 

 and more compact forms they are 

 mucilaginously thickened. The 

 thalli of the Corattinaceae, which 

 have the form of branched fila- 

 ments or of flattened or tubercu- 

 late incrustations, are especially 

 characterised, on the other hand, 

 by their coral -like appearance, 

 owing to the large amount of calcium carbonate deposited in their cell 

 walls. The calcareous Florideae are chiefly found on coasts exposed to 

 a strong surf, especially in the tropics. 



The Rhodophyceae are usually red or violet ; sometimes, however, 

 they have a dark purple or reddish-brown colour. Their chromatophores, 

 which are flat, discoid, oval, or irregular-shaped bodies and closely 

 crowded together in large numbers in the cells, contain a red 

 pigment, phycoerythrin, which completely masks the chlorophyll. 

 True starch is never formed as a product of assimilation, its place 

 being taken by other substances, very frequently, for example, by 

 Floridean starch. The cells may contain one or several nuclei. 



Reproduction is effected either asexually by means of spores, or 

 sexually by the fertilisation of female organs by male cells. 



The asexual spores are non-motile ; they have no cilia and are simply naked, 

 spherical cells. They are produced, usually, in groups of four, by the division of a 

 mother cell or sporangium, from which they are in time set free by the transverse 

 rupture of its walls. The sporangia themselves are nearly spherical or oval bodies 

 seated on the thalloid filaments or embedded in the thallus. In consequence of 

 their usual formation in fours, the spores of the Florideae are termed tetraspores 

 (Fig. 261). They are analogous to the swarm-spores of other Algae; similar 

 spores are found also in the Dictyotaceae among the brown Algae. 



In the development of the sexual organs, particularly the female, the Rhodo- 

 phyceae differ widely from the other Algae. Batrachospermum moniliforme, a 

 fresh- water form, may serve as an example to illustrate the mode of their formation. 



