294 XXII. REPRODUCTION OF ALGM. 



now withdraw towards the interior of the polygonal sections, and 

 these latter -appear bounded towards one another by clear lines. 

 The sections then begin to round off, and so partially to separate 

 from one another. The colourless peripheral protoplasm takes 

 no part in the differentiation of the chlorophyll-containing con- 

 tents into individual sections, but is transformed into a colourless 

 mucus, which plays a part in the evacuation of the swarm-spores 

 (zoospores), 



The evacuation of the swarm-spores arises from the pressure 

 of the cell-contents upon the gelatinous papilla, which they break 

 through. Individual swarm-spores may also 

 remain behind in the sporangium. If the ob- 

 ject is examined in a suspended drop, under 

 the influence of light, the swarmers ultimately 

 collect either at the side of the drop turned 

 towards, or at that turned from, the window. 

 FIG. 108. Clado- These swarmers are not, however, amongst 



phwa glomerata. A . . . 



swarm-spore fixed with those most sensitive to light; they remain for 



!ld e i s fte ey" a lon g<* time Mattered in the drop, move about 



spot ; in the anterior i n indefinite directions, and only gradually, as 



colourless portion the , ,..., . , , -. 



nucleus is to be seen their motile energy diminishes, arrive at the edge 

 of the drop, where they come to rest. They 

 then round off, and surround themselves with a cell- wall. The 

 swarm-spore is pear-shaped, with a red eye-spot placed laterally 

 by the colourless or green anterior " beak ". The eye-spot is most 

 readily recognisable with the use of a substage condenser and the 

 diaphragm wide open. With a little iodine these swarm-spores 

 can be very readily fixed (Fig. 108). We recognise now two cilia 

 upon each (in other species of Cladophora, even four), which 

 arise from the tapering anterior beak of the swarm-spore. The 

 swarm-spores move with the ciliate end forwards. In swarm- 

 spores lying in a favourable position, the small nucleus is thor- 

 oughly recognisable, after treatment with iodine, lying in the 

 anterior colourless end (compare the figure) ; the nucleolus usually 

 stains very sharply. 



These swarm-spores which we are studying are asexual, but 

 in Cladophora still other, smaller, sexually differentiated swarmers 

 or Gametes, are produced. These conjugate with one another, 

 but have hitherto been observed only in the marine forms. The 

 larger, asexual, swarm-spores have in these latter four cilia the 

 smaller gametes only two. 



