2 FIRST GROUP. THALLOPHYTES. 



Bryopsis and Codium are known to have two kinds of swarm-spores, small yellow 

 and larger green ones, but no sexual act has at present been observed. If the suppo- 

 sition should be confirmed, that the smaller motile cells are male, and the larger female, 

 we should then have a transition established to those Siphoneae in which there is 

 oogamous fertilisation, and especially to Vaucheria, which as yet stands somewhat 



isolated. 



Vaucheria 1 consists of a variously branched tube, sometimes thirty centimetres long, 

 which grows in shade on damp soil, or in water both fresh and brackish. Its fixed end 

 (rooting-end) is hyaline and contortedly branched. The free portion contains within 

 its thin & cell-wall a layer of protoplasm, rich in chlorophyll-granules and oil-drops, and 

 enclosing a large sap- cavity. The oil-globules appear from Borodin's investigation of 

 V. sessiUs to be assimilation-products ; they lie outside the chlorophyll-bodies but are 

 probably formed in them. The plants are produced at the commencement of the 



FIG. 14. Vaucheria sessih's (magnified about 30 times). Description in text. 



period of vegetation in spring from oospores of the previous year, and in many species 

 they propagate themselves at first asexually during several generations. The brood- 

 cells which serve to this end are either obtained by simple abstriction of the ends of 

 certain twigs, or they are large swarm-cells which escape from the tube, and have their 

 whole surface clothed with very short cilia. The various species of Vaucheria show 

 graduated transitions from the one of these forms to the other. For instance, in 

 V. tuber osa branches swell up to a considerable size, become detached at the bases, and 

 put out at once one or more genninating tubes. In V. geminata the contents of a 



1 Pringsheim, Ueber Befruchtung u. Keimung der Algen u. das Wesen des Zeugungsprocesses 

 (Monatsber. der Berliner Akad. d. \Viss. 1855, and Jahrb. f. wiss. Bot. II. p. 470). Schenk, Entw- 

 der Fortpflanzungs-Organe u. Befruchtung von Vaucheria geminata (Verh. der physik.-med. Ges. zu 

 Wiirzburg, Bd. VII. 1853"). Walz, Beitr. zur Morph. und Syst. d. Gatt. Vaucheria (Pringsheim's 

 Jahrb. V. Bd.). Woronin, Beitr. zur Kenntn. d. Vanch. (Bot. Zeit. 1869), and Vaucheria de 

 Baryana (Bot. Zeit. iSSo). Stahl, Ueber d. Ruhezustande d. V. geminata (Bot. Zeit. 1879). With 

 respect to the nuclei see Schmitz und Strasburger, loc. cit. Borodin, Ueber die Wirkung des Lichtcs 

 auf die Entwicklung von V. scssilis (Bot. Zeit. 1878, p. 497). 



