310 Mr. J. Ralfs on Spirulina and Coleochsete. 



of series of cells radiating from a centre and connected together 

 by a hyaline substance ; spores imbedded in the frond*. 



1. C. scutata, Br^b. Cells having on their upper surface a cylin- 

 drical truncate sheath, from which a bristle at length protrudes. 

 Breb. Ann. d. Sc. Nat. s^rie 3. vol. i. p. 29. tab. 2. 

 In pondsj parasitic on aquatic plants, especially on the under sur- 

 face of the leaves of Potamogeton nutans and Nymphcea alba when 

 verging to decay. Victoria Park, Manchester, and in Windermere, 

 Mr. Sidebotham ; Aberdeen, Dr. Dickie ; Henfield and near Tun- 

 bridge Wells, Sussex, Mr. Jenner ; near Fleetwood, Mr. J. S. Ash- 

 worth ; near Bristol, Mr. Thwaites ; ponds at Singleton and Sketty 

 near Swansea, Mr. Moggridge ; also abundant in Cromlyn Bogs near 

 the same town. In several stations near Penzance and Dolgelley. 



This parasite, I suspect, is not uncommon, but from its mi- 

 nuteness it is difficult to detect, especially when growing on leaves 

 which still remain slightly green. It was first gathered in this 

 country by Mr. Sidebotham, who kindly sent me specimens ex- 

 ceedingly well-mounted. 



The very minute fronds, which to the naked eye seem mere 

 specks, are under the microscope found to consist of many series 

 of cells radiating from a centre and connected together by a co- 

 lourless substance, which is best seen at the margin. Each series 

 of cells is repeatedly dichotomous ; the cells are longer than broad 

 and truncate, the four or five central ones somewhat irregular, 

 the others of equal length, forming concentric circles. These 

 circles vary from five to twenty in number. Endochrome greeii, 

 and usually contracted into a central spot in each cell. 



After some time a cylindrical, colourless process appears on 

 the upper surface of each cell ; it is directed outwards and is trun- 

 cate at the extremity ; within it a bristle becomes visible, gra- 

 dually protrudes, and finally becomes much elongated. The 

 bristle sometimes contains pale granular matter, when it may be 

 traced even before it issues from the tube. Before the protrusion 

 of the bristle the sheath is always truncate, as if open at the end, 

 but afterwards it is sometimes conical, as if a membrane was 

 pushed out and then perforated. 



Although the fronds are closely appressed, if care be used they 

 may generally be separated by a penknife from the leaf on which 

 they grow. The margin of the frond is well-defined ; in young 

 plants it is usually circular, but in the larger specimens often 

 slightly lobed. 



The spores, which are imbedded in the frond, are suborbicular 



* " Frons disciformis, adpressa filarnentis e centro radiantibus ssepius 

 coadunatis ; formata filamenta articulata dichotomo-vamosa edorso articulo- 

 rum vaginas cylindricas, truiicatas longe setigeras passim prodeunt. Endo- 

 chromas viride." — Breb. Ann. d. Sc. Nat. serie t3. vol. i. p. 29. 



