lY- CHORDARIACE^.— Leathesia. 129 



IV. LEATHESIA. S. F. Gray. 



Frond globose or lobed, solid or at length hollow, consisting of filaments radiating 

 to all sides from a central point. Axis composed of oblong colourless cells, united 

 in dichotomous threads which issue from a common base ; the uppermost cells half- 

 moon shaped. Peripheric filaments issuing from the outermost axial cells, simple, 

 moniliform, strongly glued together, with globose articulations. Spores obovoid 

 or pyriform, aflixed at the base of the peripheric filaments (with which they have a 

 common origin) and concealed among them. 



Very unlike the preceding genera in external characters, but closely allied in 

 structure to Mesogloia, particularly to M. vermicularis. Leathesia indeed chiefly 

 differs from Mesogloia in having the frond irregularly lumpy or tuberous, instead 

 of cylindrical and branching. The following species has a very wide geographical 

 range, being a common inhabitant of the shores of both hemispheres. East and 

 "West, and also of the Southern Ocean. It abounds at least at the Cape of Good 

 Hope. 



1. Leathesia tuberiformis, Gray ; fronds olivaceous, tuberous, when young 

 stufied with cottony fibres (the axis), at length hollow. Harv. Phyc. Brit. t. 324. 

 Leathesia marina, Endl. — J. Ag. Sp. Alg. vol. 1, p. 52. Kiltz. Sp. Alg. p. 543. 

 Corynephora marina, Ag. — Bivularia tuberiformis, E. Bot. t. 1956. (Tab. X. C.) 



Hab. On rocks and Algae between tide marks. At Halifax, W. H. H., (v. v.) 



Fronds clustered together, varying in size from the bigness of a pea to that of a 

 large walnut, irregularly lobed and bullated ; at first solid but becoming hollow 

 from the perishing of the cottony axial filaments. The frond then consists merely 

 of the peripheric filaments, which are strongly glued together and constitute the 

 whole substance of the walls of the then hollow tuber. They can be sej)arated only 

 by using considerable pressure. The plant makes its first appearance in April or 

 May, and in August or September attains its full size and produces fruit, decaying 

 soon after. 



Plate X. C. Fig. 1 . Cluster of fronds of Leathesia tuberiformis, on a piece of 

 rock, the natural size ; fig. 2, vertical section of a frond, showing a small portion of 

 the periphery, and some of the axial filaments, magnified ; fig. 3, peripheric filaments 

 supported on the apical cells of the axial filaments ; fig. 4, a spore and two peripheric 

 filaments, both the latter figures highly magnified. 



VOL. HI. ART. 4. 



