THE ALG^E 



115 



tents escape as numerous small biciliate gametes (F), which after conjugation 

 germinate at once. A similar, but more complicated, type of reproduction 

 occurs in the marine genus Acetabularia. In Codium and Bryopsis biciliate 

 cells of two kinds are formed in special cells (Fig. 85, C). While the actual 

 fusion of these cells has not been seen, it is highly probable that they are 

 gametes. The larger ones are green, the smaller ones yellowish, in color. 



The most highly developed reproductive organs occur in Vaucheria (Figs. 88, 

 89), where antheridia and oogonia of characteristic form are present, and the 

 egg-cell has lost the power of motion and is retained within the oogonium. The 

 latter is an oval cell, with a more or less definite beak at the apex. The anther- 

 idium is an elongated, often curved, cell, which may arise directly from a 

 vegetative filament, or 

 may be borne with the 

 oogonium (or oogonia) 

 upon a special branch 

 (Fig. 89). 



The young oogonium 

 contains numerous nu- 

 clei, but before it is shut 

 off from the filament, all 

 but one of these retreat 

 into the filament, leaving 

 but a single nucleus in 

 the oogonium. When 

 ripe, the latter opens at 

 the apex, and a portion 

 of the contents is ejected, 

 the remainder forming 

 the egg (Fig. 89, C, D). 



In the antheridia, 

 which contain little or 

 no chlorophyll, numer- 

 ous minute spermato- 

 zoids are developed. They consist mainly of a nucleus, and possess two 

 laterally inserted cilia. One of them penetrates the egg and effects fertilization. 

 The egg now develops a thick membrane, loses its chlorophyll, and becomes 

 a resting-spore. This germinates by sending out a germ-tube, much as does the 

 zoospore. 



Classification of Siphoneae (Engler and Prantl, 9) 



As the development of many of the Siphoneae is still imperfectly 

 known, their affinities are still somewhat doubtful. The following 

 families are recognized: Botrydiaceae, Phyllosiphonacese, Bryopsi- 

 daceae, Derbesiaceae, Vaucheriaceae, Caulerpaceae, Codiaceae, Valonia- 

 cese, Dasycladaceae. The Botrydiaceae can be readily compared to the 

 Protococcaceae, while Vaucheria suggests some of the multinucleate 

 forms among the Confervoideae, especially the genus Pythophora. 

 The affinities of most of the marine Siphoneae are doubtful. 



Phyllosiphon. A very remarkable form is the genus Phyllosiphon, 

 which resembles, in structure, Vaucheria, but is a parasite within 

 the tissues of a species of Arisarum. In habit it closely resembles 



r i 



FIG. 87. (Jaulerpa plumaris. ^Natural size. ) 



