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II. — On a Part of the Life-cycle of Clathrocystis seruginosa 

 {Kutzinfs Sioecies). By Professor P. Martin Duncan, M.B. 

 (Lond.), F.E.S., F.H.M.S., &c. 



(Read 10th December, 1879.) 



Vast quantities of this beautifully green Palmellaceous fresh-water 

 alga have lately obstructed the sand-filtering beds, attached to one 

 of the great reservoirs of drinking water, in the neighbourhood of 

 Leicester. Owing to the kindness of Mr. iVlderman Paget of that 

 town, I have had the opportunity of studying some poiuts in the 

 history of the form, which is evidently that microscopic gelatinous 

 body with green gonidia, which from its rarity excited the atten- 

 tion of Henfrey in 1856, and was described by him in ' Trans. 

 Micr. Soc. Lond.,' vol. iv. p. 53. 



The whole of the literature of the form and its synonyms were 

 detailed in that essay, and therefore it is not necessary to refer to 

 them, but simply to recapitulate the characteristics and that part 

 of the natural history which was then knowu. Henfrey gives the 

 following generic diagnosis of " Clathrocystis : — Frond, a micro- 

 scopic gelatinous body, at first solid, then saccate, ultimately 

 clathrate (fragments of the broken fronds occurring in irregularly 

 lobed forms), composed of a colourless matrix, in which are em- 

 bedded innumerable minute gonidia, which multiply by division 

 within the frond as it increases in size. No zoospores or resting 

 spores observed. 



" Clathrocystis seruginosa. — Fronds floating in vast strata upon 

 fresh- water pools, forming a bright green scum, presenting to the 

 naked eye a finely granular appearance : when dried appearing 

 hke a crust of verdigris. Gonidia of green cells, with a distinct 

 membrane, ^jj-^ inch in diameter, leaving a hyaline border at the 

 surface of the fronds. Full-grown fi-onds ^ o to ^^ inch in diameter. 

 On fresh-water lakes." 



Henfrey remarks that " this remarkable form does not appear 

 to have been observed hitherto in Britain. We found it in the 

 autumn of 1855, forming a scum, extending over a large portion 

 of the surface of the lake in the lioyal Botanic Gardens at Kew. 

 A portion of it, brought home and preserved in a room in a basin 

 of water, continued to grow healthily imtil the middle of winter." 

 The same observer states that as the growth l)y division of gonidia 

 into two or four, occurs principally at the periphery, the frond 

 becomes hollow : then the outside gives way, and as growth 

 proceeds, orifices and a clumsy lattice-work appearance occur. 

 He describes the ragged lobes being broken into irregular 

 fragments, and that each rccoiumencos the ex[-imding growtli, and 

 in time becomes a latticed frond. He moreover notices that the 



VOL. III. 



