ALGAE.— RHODOPHYCEAE. 



75 



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, Delessena) it assumes the outline of a foliage- 

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

 [Sphaerococciis, Gelidium), it is filiform or like a narrow 

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

 all these cases the growth, according to Nageli ', 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 ^dheres 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 ceil. 



Asexual reproduciwn 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 PolysopJmtia van'ega/a, not so un- 

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



DeUsser 



( ll'orm 



sijotdia) saiijriiiiicit. Ueaf-like 

 thallus with disk of .ittachinent ; 

 right and left are the bases of two 

 other leaf-like branches. 



Neuere Algensysteme, p. 24S. 



