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

 Alga. (Second Paper J. By George Shadbolt, Esq. 



(Read October 22, 1851). 



In order to ascertain something further than I was able to lay 

 before you in May last, when I drew attention to this subject, which 

 appeared to me so full of interest, I availed myself of every oppor- 

 tunity which presented itself during the past summer, of procuring 

 specimens of Algce in conjugation, and have in consequence ascer- 

 tained one or two additional facts, which I am desirous of placing on 

 record. 



Having procured a favourable specimen of Zygnema varians, in 

 which the process of conjugation was complete, the sporangia being 

 of a somewhat ovoid form, and consisting of a compact and appa- 

 rently homogeneous dark green mass, still contained within the 

 walls of the cells composing the filamentous frond ; the first change 

 which I noticed occurred after the lapse of about a fortnight, when 

 several semitransparent vesicles began to appear, here and there, in 

 some of the sporangia, gradually increasing in number, until the 

 whole of a sporangium in which the transformation was progressing 

 became converted into a vesicular mass, much resembling in ap- 

 pearance the parenchyma of an orange. (Plate XXII. fig. 2, a a). 



The vesicles first appeared just within the outer integument of 

 each sporangium, and extended over its interior surface, until a com- 

 plete layer of vesicles was formed, when another layer was produced 

 within the first, and so on, until the whole of the interior mass had 

 undergone a similar conversion. In about another fortnight, many 

 of the sporangia had assumed a beautiful stellate form, with numer- 

 ous and long projecting spines ; and were still retained within the 

 original cell-walls of the filaments, with the unaltered, or only par- 

 tially altered, sporangia in the same frond. 



There is another fact worthy of note, that whereas in Zygnema 

 quadratum, immediately upon the completion of the conjugation, a 

 considerable inflation of the receiving cell may be observed ; which, 



