OEDOaONItTM. 275 



Note that the entire filament consists of a single row 

 of cells. Here and there a cell may show, at its upper 

 end, a series of parallel transverse marks the " caps " 

 characteristic of Oedogonium. Each cell contains a 

 parietal chloroplast having the form of a network with 

 large meshes what appear at first sight to be individual 

 chloroplasts are thickenings of the network. Associated 

 with the chloroplast are pyrenoids and starch grains. 

 Note also the protoplasm layer lining the wall ; the fair- 

 ly large nucleus, with a distinct nucleolus ; the central 

 vacuole of cell-sap. 



Some of these points can be made clearer by (1) plasmo- 

 lysing a filament with salt solution ; (2) treating with 

 iodine ; (3) treating with chlor-zinc-iodine ; (4) declorising 

 with alcohol and staining with various reagents and stains. 



393. Reproduction. It is difficult to make a success- 

 ful series of observations from which to piece together the 

 somewhat complicated life cycle of Oedogonium. An 

 attempt should at least be made to observe the zoogonidia 

 and the young plants formed by their germination ; the 

 antheridia ; the oogonia in different stages ; and the dwarf 

 male plants. 



394. The zoogonidia are formed singly from ordinary cells, 

 the contents of this cell (zoogonidangium) contract and escape 

 (by the formation of a transverse rupture of the wall) as a pear- 

 shaped zoogonidium with a circle of cilia at its clear narrow 

 anterior end. After a motile period, the zoogonidium becomes 

 attached by the clear anterior end, forms a cell-wall, and grows 

 into a new filament ; the young plants may be found on the sides 

 of the vessel containing the material with zoogonidia, or on glass 

 slides dipped into or suspended in the water, or attached to plants 

 or stones in ponds, etc. , with mature Oedogonium plants. 



395. Oogonia may be formed from any of the cells, either 

 singly or in series one above another ; the contents of the oogonium 

 (recognised by its large size and swollen form) round off to form an 

 oosphere, containing abundant chlorophyll except at the clear 

 receptive spot which faces the part of the wall where the opening 

 will be formed the opening may take the form of a circular split 

 or a pore (at top, base, or middle of oogonium), or a lid may be 

 detached. 



