ALGAE. RHODOPHFCEAE. 



75 



A 



escapes from injured cells. The red and the green colours in the Florideae agree 

 very closely in their optical properties. 



The thallus consists in the simplest species of branched cell-rows, which 

 elongate by growth at the apex with transverse segmentation of their apical cells. 

 In many Ceramiaceae there is an apparent formation of tissue ; branches from the 

 mother-axes grow closely applied to them and invest them with a cortex ; so that 

 here, as in Chara and the Phaeosporeae, there are species in which tissue is formed 

 by the coalescence of branches originally separate. In other Florideae the thallus is 

 a cell surface of one or sometimes several layers; in many 

 (Hypoglossum, Delesserid) it assumes the outline of a foliage- 

 leaf, and even shows venation (Fig. 47) ; in others, again 

 (Sphaerococcus, Gelidtuni), it is filiform or like a narrow 

 ribbon, and is much branched (Plocamium and others). In 

 all these cases the growth, according to Nageli 1 , is apical 

 by means of an apical cell ; in the simpler forms the seg- 

 mentation is by transverse division, in others two to three 

 rows of cells are formed by oblique septa. One section with 

 many species, the Melobesiaceae, a subdivision of the Coral- 

 lineae, has a disc-shaped thallus, which grows centrifugally 

 at the circumference (Fig. 46), and adheres closely to the 

 object on which it grows, usually larger Algae. These species 

 have therefore some resemblance to Coleochaete scutata, but 

 their thallus is many-sided, and its cell-walls are incrusted 

 with lime. This feature is more evident in other Corallineae, 

 the ascending branches of which have a number of initial 

 cells, and not a single apical cell. 



Asexual reproduction is effected by means of non- 

 motile gonidia, four of which are often formed in one 

 mother-cell, and are therefore called tetraspores, or more 

 correctly tetragonidia ; sometimes the mother-cell produces 

 only one, sometimes two, sometimes eight gonidia ; they 

 are altogether absent in the Lemaneae. If the thallus con- 

 sists of cell-rows, the tetragonidia are formed in the terminal 

 cell of lateral branches ; in other cases they lie imbedded 

 in the tissue of the thallus, and not unfrequently in special 

 branches of it and in large numbers (Fig. 48, /); these 

 branches have been called stichidia. 



The sexual organs are usually found on plants which 

 do not form gonidia, and these plants are monoecious 

 or dioecious ; but both kinds do occur at the same time 

 on the same plant, and in some species, as in Polysophonia variegata, not so un- 

 commonly. The account which Sirodot gives of the fresh-water Batrdchospermum is 

 remarkable and requires further investigation. He says that the germination of the 

 carpospores does not result in the direct production of a batrachospermum-plant, but 



FIG. 47. Dclcsscria (Worm 

 skjoldia) sanguinea. Leaf-like 

 thallus with disk of attachment ; 

 right and left are the bases of two 

 other leaf-like branches. 



1 Neuere Algensysteme, p. 248. 



