40 RhodophycecB 



Genus Thorea Bory, 1808. This is a rare genus with only 

 one species Th. ramosissima Bory which, although found in 

 several of the rivers of France and Germany, has only once been 

 recorded for Britain (from Walton-on-Thames). It has a round 

 filamentous thallus, which is much branched and reaches a length 

 of 30 60 cms. It is about the thickness of a horse-hai r , of a 

 purple-brown or dark brown colour, and very mucous. There is a 

 central solid axis consisting of filaments of cells, and arising from 

 this axis are a very large number of short compact branches, which 

 are slightly attenuated. The cells of the branches are from two 

 to five times longer than their diameter. Schmidle 1 has recently 

 worked out much of its structure and fructification, and this has 

 been largely confirmed by Hedgcock and Hunter 2 . This genus has 

 been placed under the Phseophycese, but the pigment, the presence 

 of starch-like granules in the cells, and the naked non-motile 

 spores, indicate a near relationship with certain of the Floridea?. 



Family 2. LEMANEACE.S3. 



This is a small group of exclusively freshwater Algae including 

 the two genera Lemanea and Sackeria. They are plants which 

 only grow in rapid torrents, occurring attached to the rocks of 

 waterfalls, to stones and wood in mill-sluices, etc., always where 

 the force of the water is greatest. The thallus is composed of a 

 basal, attached portion, termed by Sirodot 3 a " systeme radicant," 

 from which arise csespitose tufts of erect, branched, simple fila- 

 ments reaching a length of 3 8 mm. From portions of these 

 filaments the fructiferous branches arise. These are the most 

 conspicuous and important parts of the plant, in most species the 

 vegetative portion dying away after their production, and in a short 

 time they become fixed by organs of attachment of their own. 

 Each species is thus represented by two distinct sets of indi- 

 viduals, the one vegetative and the other reproductive. 



The fructiferous branches are elongated, thread-like portions 



1 Schmidle, ' Uutersuchungen iiber Thorea ramosissima Bory,' Hedwigia, Bd 

 xxxv, 1896. 



2 G. G. Hedgcock and A. A. Hunter in Botan. Gazette, xxxviii, 1899. 



3 Sirodot, ' Etude anatomique, organogenique, et physiologique de la Fam. des 

 Lemaneacees,' Ann. Sci. Nat. Bot. torn, xvi, Paris, 1872. 



