IV. 
CHORD ARIACEiE. — Leathesia. 
129 
IY. LEATHESIA. S. F. Gray. 
Frond globose or lobecl, 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, affixed 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 
stuffed with cottony fibres (the axis), at length hollow. Harv. Phyc. Brit. t. 324. 
Leathesia marina , Endl. — J. Ag. Sp. Alg. vol. 1, p. 52. Kiitz. Sp. Alg. p. 543. 
Corynephora marina, Ag. — Rivularia tuberiformis, E. Bot. t. 1956. (Tab. X. C.) 
Hab. On rocks and Algse 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 separated 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. 
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VOL. in. ART. 4. 
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