62 
THE SEAWEEDS 
usually horizontal, mostly flat, with a midrib. Vesicles formed by modifi- 
cation of a single small leaf, spherical or ellipsoidal, naked or crowned by 
a mucro or leaflet. Receptacles formed by morphosis of a single leaf in 
the axil of another supporting leaf, and when mature carrying the con- 
ceptacles. Conceptacles excavated beneath the surface of the receptacle 
but communicating with the surface by a canal, mostly hermaphrodite. 
Antheridia small, rounded, racemose. Oogonia monosporous. 
A genus of world-wide distribution including nearly 80 Australian 
species, grouped in three subgenera — Plnjllofricha, ArtJirophycus , and 
Eusargassum. 
Subgenus Phyleotricha (Aresehoug) J. Agardh. 
Fronds formed by the evolution and repeated division of a primordial 
pinnate leaflike axis, the parts of which by transformation bear proper 
leaves, vesicles and receptacles. Leaves pinnatifid, the lower segments 
broader, the upper narrow, often ramelliform. Vesicles minute ellipsoidal- 
like swellings in the lamella and beaked (aristate), or larger terminal 
rounded and unbeaked (mutic). Receptacles terminal, smooth, at length 
racemose on a ramulus. 
There are four Sections of Phyllotricha — Heteromorphae, Cladomorphae , 
Phyllomorphae, and Pteromorphae. All are confined to Australia- Tasmania. 
Fig. 40. — ■Surgas&um heteromorpTmm. 
