42 RTiodophycece 



row of tubular cells surrounded by rows of smaller cortical cells, 

 growth taking place in all cases by an apical cell. The only 

 known method of reproduction is a sexual one. The antheridia 

 are short, cylindrical cells developed on the exterior of the thallus, 

 either on verticillate eminences or on the widest parts of the 

 nodes. The procarp is unicellular and the carpogonium possesses 

 a rather long, transparent, simple or branched trichogyne. After 

 the fertilization of the carpogonium an ooblastema-filament is 

 developed from it, at the extremity of which a bunch of jointed, 

 moniliform filaments arise. Each of the swollen cells of these 

 moniliform filaments becomes, when mature, a carpospore. 



The carpospores are thus produced inside the thallus, filling 

 up the space between the central axis and the cortical cells 

 of the fructiferous filaments. On development the carpospores. 

 produce the vegetative thallus, a protonema-like growth which has 

 frequently been mistaken for a form of Ckantransia. 



Genus Lemanea Bory, 1808. The vegetative thallus generally 

 persists for several months, and is very branched but never pili- 

 ferous. The fructiferous filaments are torulose, being regularly 

 inflated at even distances, and are normally simple. The central 

 axis of tubular cells is surrounded by a series of spirally twisted 

 axial filaments, and the antheridial areas are in more or less com- 

 plete rings round the nodes. 



L. torulosa Kiitz. ; em. Sirodot (fig. 3 C, D), and L. parvula Sirodot, are 

 found in the rapid streams and torrents of certain parts of the British Isles. 



Genus Sacheria Sirodot, 1872. The vegetative thallus is very 

 fugacious. It is little branched, often piliferous, and exists for 

 about a month (generally December or January). The fructiferous 

 filaments are cylindrical or setaceous and usually branched. The 

 central axis of tubular cells is quite devoid of axial filaments and 

 the^ antheridial areas are on mamilliform projections, arranged in 

 a verticillate manner at regular intervals. 



Species of this genus are much more frequent than species of Lemanea* 

 Three species of the genus are widely distributed in the British Isles, 

 S. fluviatilis (Ag.) Sirod. (syn. Lemanea fluviatilis Ag.), S. fucina (Bory) 

 Sirod., and S. mamillosa Sirod. (fig. 3 A, B), the last-mentioned one being 

 the most abundant. It appears that >V. mamillosa may sometimes occur in 

 still water, as I have recently examined specimens of this species collected by 

 Mr J. Murray from the west side of Loch Ness, Inverness. It must be 

 remembered, however, that Loch Ness is a large body of water forming part 

 of the Caledonian Canal, and probably numerous currents exist in it. 



