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In Mr. Hassall's work, all the sporangia which he has figured as 

 resulting from the conjugation of the filamentous Alga are more or 

 less of a spheroidal or ellipsoidal form, with the exception of that of 

 the genus Staurocarpus, which is somewhat cubical. That such 

 forms do result is perfectly true ; but I have positive evidence that 

 in two species of Zygnema ascertained, and another species in the 

 family not ascertained, the forms figured are only the sporangia in a 

 transition state, and that they eventually become stellate, and very 

 similar to the sporangia of the Desmidiece, and to the so-called Xan- 

 thidia found in the flint, with which I entertain very little doubt they 

 will at some time prove identical. 



In the middle of the month of April, in the current year, I first 

 saw a single specimen of the sporangium, in its stellate form, of Zyg- 

 nema quadratum, to which my attention was directed by Mr. Hodg- 

 son, while examining some specimens we had just previously been 

 collecting in Hainault Forest. I imagined it was a sporangium of 

 one of the Desmidiea, and sought amongst the mass of filaments and 

 ellipsoidal fruit (which latter was very abundant), endeavouring to 

 find out to which of the Desmidiece it appertained, but without suc- 

 cess ; neither did I then discover any more similar forms. Fortu- 

 nately, however, I preserved the specimen, and some few days after- 

 wards, when again seeking amongst the filaments, observed six or 

 eight of the stellate bodies, and was not a little surprised to find one 

 specimen within the walls of a filament. 



This led me to suspect that it might possibly be a more perfect 

 form of the ellipsoidal sporangium ; and within a few days I had the 

 satisfaction of verifying the fact more distinctly ; for, having isolated 

 the mass of Zygnema quadratum, and placed it in water exposed to 

 the sun's rays, I examined it carefully, day by day, and ascertained 

 not only that the number of stellate forms rapidly increased, but ob- 

 tained them in various stages within the frond, the mass of green 

 matter being sometimes entirely and sometimes only partially converted, 

 but with sporangia in the earlier stage (that is, of an ellipsoidal figure), 

 on either side of it, in the same frond (Plate XXII. fig. 1, a, b, d, e). So 

 great was the increase of the number of the perfect sporangia during 

 the lapse of the few days, that, whereas in a search of some hours 

 I could not detect more than eight individuals when I first sought 

 for them, in about ten days afterwards I found no less than twenty- 

 six in a single slide which I mounted, consisting only of a small 

 quantity, that could be looked all over in five minutes ; and in some 

 cases the spines were bifurcated. (Plate XXII. fig. 1, c,f, g). 



