252 Dr. L. Radlkofer on Fecundation in the Vegetable Kingdom, 



hand, and of tlie true spores and gonidia on the other, but, 

 above all, from the consideration of the peculiar mode of deve- 

 lopment in each of these organs, — he declares distinctly against 

 the opinion which would estimate the spermatia only as spores 

 or gonidia*. 



The view of Leveillet, who regarded the paraphyses of the 

 Lichens as their fecundating organs, and Bayrhoffer^s;!:, who 

 ascribed a different sexual nature to the separate layers of the 

 thallusj need merely be mentioned for the sake of completing 

 the historical summary. 



3. Alg^e. 



But a few years since, exact science knew nothing of a process 

 of fecundation in the Algre. The conjugation of Spirogyra, 

 known as long ago as by Vaucher^, had indeed been taken to 

 be such ; but the asserted observation, that the formation of the 

 spore occasionally occurred without any union of the conju- 

 gating cells really having taken place, had brought the whole 

 matter into question again in the most recent tmie. Vaucher 

 had perceived the so-called horns, and even conjectured that 

 they had the import of anthers |j; but from the suspicion to the 

 experimental proof, with which alone science can be satisfied, 

 the road is often very long, and not to be traversed without 

 numerous fruitless diversions. 



* Tulasne's observations extend at the same time to the (so-called) 

 germination of the spores of Lichens, and confirm and complete in this 

 respect the statement of Meyer {loc. cit. p. 175), Fries (Lichenogr. Europ. 

 reformat. Lund, 1831, pp. Iv, Ivi), Buhse (Ueber d. Fruchtkorper der 

 Flechten, Bull. Natmforsch. Gesell. Moskau, Bd. 49, p. 32, 1846), Meiss- 

 ner (Bot. Zcitung, 1848, p. 90), IloUe (/. c p. 31), and Speerschneider 

 (Bot. Zeit. 1853, p. 721, 1854, pi. 14. figs. 10 & 11). The internal cell ot 

 the spore breaks through the cuticle — in the compound spores usually at 

 the points of the end-cells, and elongates into ramified filaments. Sub- 

 sequently se))ta appear in these, from their point of origin onwards, by 

 which they are converted into moniliform rows of cells. By interweaving 

 together, these filaments form a tolerably closely-meshed plexus — proto- 

 thallus of authors, prothallus of Tulasne, — on which, at several points, is 

 formed a layer of colourless, round cells — to judge from fig. 3. pi. 3 of 

 Tulasne's memoir, by detachment of cells produced as buds (abschniirung) 

 — as is assumed of the gonidial cells by Schacht (Pflanzenzelle, p. 135) 

 and Speerschneider (Bot. Zeit. 1853, p. 710, &c. ; 1854, p. 214, &c.). Upon 

 these soon appear cells, filled with green substance, perfectly resembling 

 the gonidial cells of the full-grown thallus. The cultivation of the young 

 plant never succeeded beyond this point. 



t Ann. des Sc. nat. 3 ser. xv. p. 120 (1851). 



:J: J. D. W. Ba^rhofFer, Einig. iiber die Lichenen und deren Befruchtung. 

 Bern, 1851. 



§ J. P. Vaucher, Histoire des Conferves d'eau douce. Geneve, 1803, 

 p. 43 et seq. \\ L. c. p. 14 et seq. pi. 2 & 3. 



