274 



Siphon odadiales 



posterior yellow chromatophore, a centrally placed nucleus and two anterior 



cilia. As many as 300 antherozoids 

 may be formed from each ' ring ' of 

 the original ccenocyte during its con- 

 version into an antheridium. They 

 finally escape through small lateral 

 apertures in the old wall. 



In each oogonium there are 

 numerous oospheres or egg-cells, dark 

 green in colour but with a con- 

 spicuous receptive spot. According 

 to Klebahn ('99) they may be either 

 uninucleate or multinucleate. The 

 antherozoids enter the oogonia 

 through minute lateral* orifices in 

 the membrane (fig. 176 Bop). After 

 fertilization the wall of the egg is at 

 first very thin, but a second verru- 

 cose wall arises underneath the first 

 one, and the conical verrucse of this 

 membrane are connected by ridges. 

 Subsequently the first membrane is 

 shed. The egg-cells become filled 

 with starch and oil, the latter having 

 dissolved in it a bright red pigment. 

 The ripe oospores rest for a long 

 time and can survive dry conditions, 

 even for several years. 



On the germination of the 

 oospore the chlorophyll becomes 

 more obvious and the contents 

 divide into 2, 4 or 8 (according to 

 Meyer, '06, always 4) parts, which 



Fig. 176. Sphssroplea annulina (Roth.) Ag. 

 A, part of ccenocyte stained to show annular 

 aggregates of small chloroplasts (ch), nuclei 

 (n) and pyrenoids (py), x 440. B, parts of 

 two coanocytes with gametes and fertilized 

 eggs, x 440. an, antherozoid ; o, oosphere ; fo, 

 fertilized egg ; op, opening through wall of 

 coenocyte. C, part of ccenocyte with ripe 

 oospores (ro) showing the verrucose walls, 

 x 440. D, one of the zoospores formed on 

 germination of the egg-cell, x 240. E and F, 

 young plants formed from germinating zoo- 

 spores, x2;sf). n, nucleus; py, pyrenoid. 

 (J5 and D 1<", after Cohn.) 



then issue from a split in the old 

 wall as biciliated oval zoospores 

 (fig. 176 D). These quickly undergo 

 a transformation into spindle-shaped 

 bodies, with much attenuated ex- 

 tremities, and soon an annular appearance of the contents is plainly visible 

 (fig. 176 F). The young plants grow rapidly in size and become much 

 elongated, acquiring numerous nuclei and pyrenoids, after which the first 

 transverse wall appears. 



