REJUVENESCENCE IN NATURE. 297 



sessilis, after the separation of the horn from the spore, 

 the former appears open at the point, and a considerable 

 space, doubtless shut off as a separate end-cell before the 

 separation, empty; the spore is at this time likewise 

 surmounted by a more or less distinct tube, empty and 

 open at the summit, which undoubtedly is the open end 

 of the mother-cell of the spore. The open end of the 

 emptied end-cell of the horn on one side, the open end 

 of the mother-cell of the spore on the other, together 

 with the fact that the two were previously connected, 

 certainly render it very probable that this connection is 

 a real conjugation, that, therefore, the contents of the end- 

 cell of the horn are united with those of the mother-cell of 

 the spore to form the spore itself. The application of the 

 horn upon the spore-bearing branch ought then to take 

 place before the formation of the spore, on which point 

 my observations are deficient, but which is in agreement 

 with Nageli, figure 21.* However, on the one hand, the 

 circumstance is puzzling that many species seem to pos- 

 sess no trace of the said open tube surmounting the 

 spore, f while other species exhibit open tubes in the 

 spore-branchlets with no horns corresponding to them, 

 as, for instance, V, polysperma, Hassall,} with very 

 numerous, linearly arranged spores, but only very few 



* See, on this point, Karsten on ' Conferva fontinalis, L.y in tbe 

 ' Botanische Zeituiig,' 1852, p. 89, et seq., pi. 1, wherein he describes the 

 conjugation in all its stages. A. H. 



f Thus, for example, in Vamheria terrestris and hamata, in which, at the 

 same time, in spite of the strange position of the spore on the back of the 

 horn, an union of the inrolled point of the horn with the spore does occur, 

 as is represented very beautifully, and even with emptying of the end- 

 cell of the horn, by Thuret, ('Sur les Org. Locomot. des Spores des 

 Algues,' 'Ann. des So. nat.,' 2d ser., vol. xix, t. 15, f. 49, (1843,) in a form 

 doubtless belonging to V. hamata. In V. geminata the little tube above the 

 spore is likewise wanting, but Nageli has seen a scar on the summit of the 

 spore, which indicates the previous union with the horn, and indeed, accord- 

 ing to Hassan's observations, not with the point but with the side of the 

 horn. The form of the horn in V. cruciata, (Vauch., 1. c., t. ii, f. 6,) nearly 

 allied to F. geminata, is interesting, since two little side horns issue from 

 the principal horn, from their position evidently destined to union with the 

 two spores. 



\ L. c., t. 4, f. 6. I have observed this species also near Freiburg. 



