SECT. I 



CRYPTOGAMS 



375 



ing of single rows of cells {e.g. Callithamvion). In other cases the 

 branched filamentous thallns appears multicellnlar in cross-section. 

 In many other forms the thallus is flattened and ribbon-like {e.g. 

 Chondrws crkpus, Fig. 300; Gigarfina mamiUosa, Fig. 301); while 

 in other species it consists of expanded cell surfaces attached to a 

 substratum. All the Florideae are attached at the base by means 

 of rhizoidal filaments or discoid holdfasts. One of the more com- 

 plicated forms is Delesseria san guinea {Hydrolapathnm) (Fig. 9), which 

 occurs on the coasts of the Atlantic. The leaf-like thallus which 

 springs from an attaching disc is provided with mid ribs and lateral 

 ribs. In the autumn the wing-like expansions of the thallus are 

 lost, but the main ribs persist and give rise to new leaf-like branches 

 in the succeeding spring. The 

 thalli of the Corallinaceae, which 

 have the form of branched fila- 

 ments or of flattened or tuber- 

 cnlate incrustations, are especi- 

 ally characterised by their coral- 

 like appearance, owing to the 

 large amount of calcium carbonate 

 deposited in their cell walls. The 

 calcareous Florideae are chiefiy 

 found on coasts exposed to a 

 strong surf, especially in the 

 tropics. 



The Rhodophyceae are usually 

 red or violet ; sometimes, how- 

 ever, they have a dark purple 

 or reddish -brown colour. Their 

 chromatophores, which are flat, 

 discoid, oval, or irregular-shaped ^"'- ^^'^--G^of-tina mummosn. s, 



IT. 11 , ° - , •'^ cvstocarps. (I iiat. size.) 



bodies and closely crowded to- . i . 



gether in large numbers in the cells, contain a red pigment, piiyco- 

 ERYTHRIN, which completely masks the chlorophyll and appears to be 

 chemically combined with it (p. 62). True starch is never formed as 

 a product of assimilation, its place being taken by other substances, 

 very frequently, for example, by Floridean starch, in the form of 

 spherical stratified grains which stain red with iodine. Oil-drops 

 also occur. 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 spokes 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. The sporangia themselves are nearly spherical 

 or oval bodies seated on the thailoid filaments or embedded in the thallus. The 

 spores escape by a transverse rupture of the wall of the sporangium.— In con- 



2 B 2 



Wart-slmped 



