324 



BOTANY 



isolated or they may be united in groups of two or more ; but under some circum- 

 stances they produce short, branched cell filaments. 



Cladophora is a genus comprising numerous species, including Gladophora glom- 

 erate/,, a form specially abundant in rivers. It consists of branched filaments of long 

 cells, growing in tufts attached to a support, and exhibiting well-marked apical 

 growth (Fig. 6, p. 12). The cells, unlike those of Ulothrix, are multinuclear, and 

 contain also numerous polygonal, closely-crowded chromatophores (Fig. 60, p. 59). 

 By the protrusion and elongation of lateral outgrowths from the cells just below 

 their upper transverse walls, the filaments become extensively branched ; while, in 

 addition to their apical growth, they increase in length also by the division of the 

 cells and the formation of new transverse walls (Fig. 66, p. 64). The swarm-spores 

 of this species are biciliate (Fig. 244), and are formed in large numbers in the cells 

 at the tips of the branches, from which they escape through an opening in the upper 

 end of the lateral wall. Having completed their swarming, they become invested 



Fig. 244. — Cladophora glome- 

 rata. Swarm-spore, (x 540.) 



Fig. 245. — A, B, Oedogonium: A, escaping swarm-spores; B, free 

 swarm-spore. C, B, Oedogonium ciliatum : G, before fertilisa- 

 tion ; D, in process of fertilisation ; o, oogonia ; a, dwarf- 

 males ; S, spermatozoid. (After Pringsheim, x 350.) 



with a cell wall, and, after a period of rest, they eventually grow out into a new cell 

 filament. In other species of Cladophora, smaller, sexual swarm-spores have also 

 been observed which, as in the case of Ulothrix, fuse together in pairs in the pro- 

 cess of conjugation. 



The genera Oedogonium and Bulboehaete may be quoted as examples of oogamous 

 Confervoideae. While the thallus of the latter is branched, the numerous 

 species of Oedogonium consist of unbranched filaments, each cell of which 

 possesses one nucleus and a single parietal chromatophore composed of numerous 

 united bands. The asexual swarm-spores of Oedogonium are unusually large and 

 have a circlet of cilia around their colourless anterior extremity (Fig. 245, B). In 

 this case the swarm-spores are formed singly, from the whole contents of any 

 single cell of the filament {A), and escape by the rupture of the cell wall. For the 

 purpose of sexual reproduction, on the other hand, special cells become swollen 

 and differentiated into barrel - shaped oogonia. A single large egg -cell with a 

 colourless receptive spot is formed in each oogonium by the contraction of its 

 protoplasm, while the wall of the oogonium becomes perforated ,by an opening at 

 a point opposite the receptive spot of the egg. At the same time, other, gener- 

 ally shorter, cells of the same or another filament become converted into antheridia. 



