165 



XXX. — On the Sporangia of some of the Filamentous Fresh-water 

 Alga. By George Shadbolt, Esq. 



(Read May 21, 1851). 



In pools and ditches in open places may generally be seen, either 

 floating on the surface or nearly submerged, a mass of slimy green 

 matter, which on slight examination proves to be composed of thread- 

 like filaments ; and on closer inspection the filaments are found to 

 consist of cells, more or less elongated and cylindrical in form, and 

 united to each other by their ends. Although by the unassisted eye 

 most of the species of the filamentous Alga are scarcely distinguish- 

 able from one another, there are many genera contained in the order; 

 and in the genus Zygnema the species are extremely numerous. 



Those who are totally unacquainted with this department of bo- 

 tany will do well to refer to Hassall's ' British Fresh-water Algse,' a 

 work in which much information is given ; and, though some of the 

 opinions there expressed have since proved erroneous, it must be 

 remembered that when the work first appeared comparatively little 

 had been done in this branch of science. The facts I am about to 

 detail have been ascertained by actual observation ; and I had be- 

 lieved them hitherto entirely unknown, until corrected on this point 

 by Mr. Bowerbank, who, however, informs me that he is not aware 

 of their ever having been published. 



In Mr. Ealfs' beautiful work on the British Desmidiece, with which 

 most microscopists are doubtless familiar, a very particular and lucid 

 account is given of the conjugation of two cells, and the consequent 

 production of a sporangium resulting from the absorption of the en- 

 dochrome contained within them. A similar effect takes place with 

 most, nay, I believe with all, of the filamentous Algce ; but in this 

 case the union takes place sometimes between cells of the same fila- 

 ment, and sometimes between those of different filaments. In some 

 instances the union of the cells is effected by the intervention of lit- 

 tle tubular passages, thrown out for that special purpose, and in 

 others directly, without the intervention of such tubes. 



