Botanical Society of Edinburgh. 



253 



1 . Homceocladia anglica, Ag. There prevails considerable confu- 

 sion regarding the plant sent by Mr. Ralfs under this name. It is 

 the Microcoleus marinus or Harvey. By some it has been looked 

 upon as Schizonema xylodes, and by others as Oscillatoria chthono- 

 plastes. From a comparison made with specimens in Mr. Berkeley's 

 Herbarium, Mr. Ralfs is satisfied that his plant is the true Homceo- 

 cladia anglica, and as such he sent specimens to the Society's Her- 

 barium. 



2. Desmidium compressum, n. sp. Filaments compressed; joints 

 rather broader than long, deeply divided. 



Pools Chyan-hal Moor near Penzance, andTowednack Moor near 

 St. Ives. 



This very remarkable and distinct Desmidium is not scattered like 

 the other species in loose bundles, but entangled among the leaves 

 of aquatic plants. It is very gelatinous, more so, in fact, than any 

 hitherto discovered ; but its mucus is not condensed into a sheath 

 as is that of D. mucosum and D. cylindricum. 



The filaments are much compressed, and therefore appear nearly 

 plane under a lens. The joints are so deeply divided, that at first 

 sight a single one might be mistaken for two. This is more especially 

 the case whilst the endochrome, denser in the centre, obscures the 

 view of that portion which unites the segments of the frustule ; but 

 as soon as the joint becomes empty, its nature is distinctly seen. 

 Though in other respects symmetrical, one segment of the frustule 

 is sometimes much smaller than the other. At the centre, where the 

 frustules join, there is a minute gland or process arising from each 

 margin. The projection of these glands is easily seen, even before 

 the frustules separate. 



A transverse view shows the endochrome to be stellate, as in the 

 other species, and also that the frustules are compressed, one dia- 

 meter being about twice as great as the other. 



Concerning this discovery Mr. Berkeley remarks in a letter to 

 Mr. Ralfs :— 



" I am quite delighted with your new Desmidium ; your observa- 

 tions are very correct. I see very distinctly the gland between each 

 pair of segments, but as there are no separate joints in my specimen, 

 I cannot quite ascertain its form. It is certainly quite distinct from 

 the other species, and is a most interesting discovery." 



Specimens of Desmidium compressum and D. Borreri were pre- 

 sented to the Society by Mr. Ralfs. 



Analysis. 



1. Filaments with a mucous sheath , 2. 



Filaments without a mucous sheath 3. 



2. Joints compressed with two angles cylindricum. 



J oints cylindrical without angles mucosum. 



3. Filaments triangular SwartziL 



Filaments cylindrical or compressed 4. 



4. Joints twice as long as broad, inflated; crenatures minute . Borreri. 

 Joints not longer than broad, compressed, deeply divided ... compressum. 



