IV. CHORD ARIACE^.—Choedaria. 123 



II. Mesogloia. Axis gelatinous, laser in the centre, composed of a network of 



filaments. Filaments of the periphery branched. 



III. LiEBiiANNiA. Axis gelatinous, denser in the centre, composed of longitudinal, 



approximated filaments. Filaments of the periphery forked. 



** Frond either tuber-shajjed or crust-like. 



IV. Leathesia. Frond tuber-shaped, cartilagineo-gelatinous. 



V. Ralfsia. Frond crust-like, spreading in round patches. 



*** Parasites, consisting of densely tufted filaments, C07inected at the base, and free above. 



VI. Elachista. Filaments pencilled, rising from a common tubercle composed of 



vertical fibres. 



VII. Myrionema. Filaments pulvinate, rising from a flat base composed of decum- 



bent fibres. 



I. CHORDARIA. Ag. 



Frond cylindrical, branched, cartilaginous, solid, at length hollow in the centre, 

 coated with a pile of radiating, horizontal, peripheric filaments. Axis formed of 

 oblong cells, connected by their ends into anastomosing, longitudinal filaments, 

 forming a compact network. Filaments oi iho. periphery at first deficient, gradually 

 evolved, and at length coating the axis in a continuous pile, densely set, club-shaped, 

 simple, moniliform, composed of spherical cells. Spores clavate or obovate, arising 

 from the base of the radiating peripheric filaments, and concealed among them. 



It is stated by Prof J. Agardh that the axis of the frond is at first hollow, and 

 that it gradually becomes solid in age, from the tube being filled up with cells. 

 I find the reverse of this to be the case. In carefully made cross sections of the 

 young frond of Ch. flagelliformis taken when the plant is an inch or two in height, 

 and long before the evolution of the peripheric filaments, I find the axis quite as 

 solid as at more advanced periods ; and I also find in old plants, but more especially 

 in Ch. divaricata, that the central cells of the axis disappear in old age, leaving the 

 frond quite fistular. This also takes place in Mesogloia, particularly in M. vermicu- 

 laris. In Ch. divaricata this hollowing of the frond of old specimens is very obvious. 



1. G'B.OKDAiRiA flagelliformis, Ag.; stem subsimple, densely set with long, lateral, 

 filiform, simple branches, which are either naked or sparingly furnished with ramuli; 



e2 



