INTRODUCTION TO C'RYPTOGAMIC BOTANY. 187 



duced either scattered or in masses, and arises from transformed 

 joints, as in some Callithamnia, a circumstance which shews a 

 close affinity to Chantransia, which differs only in the endo- 

 chrome. In Thorea the branchlets are scattered, in consequence 

 of which no knots are formed ; but the habit is the same, and 

 the purple or lilac tint assumed in drying is a confirmation of 

 its relation to Batrachospermum. In Lemanea there is a 

 most curious departure from the normal form. The threads 

 are at first precisely like those of a Conferva. Certain joints, 

 however, are protruded from the sides, after the manner of the 

 first divisions of the thread in Cladophora ; these rapidly in- 

 crease both in length and breadth, by means of transverse 

 and vertical division ; a cavity is formed in the centre ; the walls 

 are lined with large transparent cells from which articulated 

 threads are sent forth horizontally into the cavity, either from 

 every point of the surface or in whorls, insomuch that the 

 structure is almost that of a Gymopolia, or Batrachospe) niuni 

 turned inside out. The structure was described, indepen- 

 dently of each other, by Mr Tliwaites and Kutzing (Phyc. Gen. 

 p. 322, tab. 19), and is a very curious case of departure from 

 the usual cycle of growth in allied Algae. Something, however, 

 is still deficient as regards the mode of origination of the large 

 pellucid cells which line the Ulva-like tube, and the formation 

 of the central cavity. It is uncertain whether it arises by 

 absorption, or whether ceDs are formed round it. Gymopolia, 

 which abounds in calcareous matter, has the same cellular mem- 

 branous central thread as Lemanea, but the whorls of the fertile 

 threads are external, while Galaxaura, Den. (Ahjsium, Ag.) is 

 in structure almost identical, except in its calcareous matter, with 

 Thorea* The zoospores have not yet been observed. The more 

 typical species are for the most part natives of the northern 

 hemisphere, but others, as Gymopolia and Galaxaura, 

 which contain a good deal of calcareous matter, are found in 



* At least according to Decaisne's views. The figure of Ualysium 

 rugosum, by Kutzing, differs materially from the report of Decaisne, who 

 does not coincide with Kiitzing in his views as to structure. I have not 

 materials to examine the point myself. See Ann. d. Sc. Nat., 2 Ser., 

 v. 18, p. 118. I have not seen Wartmanu's Essay on Lemanea. 



