ALGAE. CONFERVOIDEAE. 



about for some time by aid of its four cilia, then conies to rest, is invested with a cell-wall, 

 and passes through a period of rest, during which it increases considerably in size. 

 In the next period of growth, a number of swarm-spores are produced from the zygo- 

 spore, but their escape from it has not yet been observed. The gametes of Ulothrix 

 can also germinate without conjugation, in the same way as the macrozoospores, but 

 they produce somewhat slenderer plants : the difference of sex is therefore not yet dis- 

 tinctly marked. Cylindrocapsa has oogamous fertilisation J ; the contents of a cell 

 of a filament which swells out into a spherical shape is rounded off into an oosphere ; the 

 small reddish male gametes (spermatozoids) make their 

 way to it through an opening in the cell-wall and effect the 

 fertilisation, no doubt by the coalescence of one or more 

 of the gametes with the oosphere. The same mode of 

 fertilisation is found in the following group, which is 

 composed of only one genus and one species ; it is re- 

 presented by 



b. Sphaeroplea annulina -, which consists in its fully 

 developed state of cylindrical filaments divided by trans- 

 verse walls into very long cells, in which green proto- 

 plasm encloses rows of large vacuoles and thus forms an 

 encircling ring. In their vegetative state the cells are all 

 alike ; it is only when sexual reproduction begins that 

 any difference appears, and then some cells produce only 

 spermatozoids, others only oospheres ; a large number 

 of the latter are formed in each cell by the breaking up of 

 its contents after certain previous changes into roundish 

 portions, each of which is marked by a hyaline spot. 

 The spermatozoids are also formed in unusually large 

 numbers by division of the contents of a cell, which has 

 previously assumed a yellowish brown colour. In both 

 kinds of sexual cells a number of holes are formed in 

 the cell-wall by absorption, and through these holes the 

 spermatozoids issue forth, and enter in crowds into the 

 cells in which the oospheres are lying. To outward ap- 

 pearance therefore the antheridia and oogonia are alike, 

 but the oospheres and spermatozoids are very unlike ; 

 the latter are elongated, club-shaped bodies, with two 

 cilia at their pointed end. The oospores invest them- 

 selves with a thick warted cell-wall, and assume a brick- 

 red colour ; their further development begins in the fol- 

 lowing spring with the division of their red-coloured 

 contents into a number of primordial cells, which escape 

 from the oospore, move about by means of two cilia, 

 come to rest, and then germinate. In this process the 

 short fusiform cell grows out at both ends into a tube, in which the posterior and 

 anterior extremities are exactly alike, and which shows therefore no distinction of base 

 and apex. After considerable increase in size transverse septa appear and the tube 

 becomes a filament composed of similar cells. The formation of (asexual) swarm-spores, 

 with the exception of those produced by the oospores, is unknown in Sphaeroplea. 



FIG. 20. Portion of a filament of 

 Ocdogonium ; at TV the cushion of cel- 

 lulose, which in Fig. B lias lengthened 

 into a piece of the cell-wall nj'\ c the 

 ' caps,' i.e. the projecting remains of 

 the earlier cell-walls which split each 

 time by an annular fissure on the out- 

 side of the cushion. 



1 Cienkowski, Zur Morphol. der Ulothricaceen (Melanges biologiques de 1'acad. de St. Peters- 

 bo'urg, T. IX. p. 534). 



a Cohn, Ann. d. sc. nat. 4^ me seiie, T. V. 1856, p. 287. [Rauwenhoff, Sphaeroplea annulina 

 (Sitzgber. d. k. Akad. d. Wiss. z. Amsterdam, 26 Mai, 1883). Heinricher, E., Zur Kenntn. d. Algen- 

 gattunq Sphaeroplea (Ber. d. deutsch. Bot. Ges. i?8?, p. -(33).] 



