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a considerable proportion of the cell-wall, and by their 

 gelatination cause an ecdysis of the outer layers of 

 cellulose. The cell-wall is usually colourless, but 

 sometimes is of a pale straw-colour or even of a 

 reddish-brown tint. It is impregnated to a certain 

 extent with lime, and an incineration of the living cells 

 leaves an ash composed chiefly of calcium carbonate, 

 a small quantity of calcium sulphate, and an insoluble 

 residue which is probably silica. 



The cell-wall is often beautifully sculptured or 

 adorned with granules, warts, processes, spines, etc. 

 In some species the wall is devoid of such embellish- 

 ments, but the cell-walls of almost all Desmids if 

 examined under a sufficiently high magnifying power 

 exhibit fine punctulations which are the optical ex- 

 pression of the pores in the cellulose wall. 



The cell-protoplasm occupies a large proportion of 

 the interior of the wall, and a portion of it always 

 completely lines the inner surface of the cell-wall. 

 This protoplasm contains numerous granules, largely of 

 a nutritive nature, and it exhibits a well-marked 

 circulatory movement. This circulation of the proto- 

 plasm is very variable and irregular, and its move- 

 ments are rendered easily visible owing to the con- 

 tained protoplasmic granules. Vacuoles are present in 

 the protoplasm, but their position and number largely 

 depend on the form of the chromatophores and the 

 general shape of the cell. There is usually a vacuole 

 in the region of the isthmus between the two chloro- 

 plasts of constricted cells, but some genera, such as 

 Closterium and Pleurotaenium, invariably possess apical 

 vacuoles. In these apical or terminal vacnoles many 

 small crystals are usually found (sometimes only one), 

 which exhibit a rapid vibratory or swarming movement. 

 These minute crystals (often rhomboidal) are composed 

 of calcium sulphate. 



When Desmids are kept alive for some time, 

 especially under abnormal conditions, the protoplasm 

 develops numerous vacuoles, often of large size, all of 



