266 SPIEOGYRA. 



380. Structure of living Spirogyra Cell (Fig. 56). 

 Place some filaments on a slide, with water, examine with 

 the low power, select those which are thickest or have few 

 or loosely coiled chromatophores (and which will therefore 

 show the details of structure most clearly), and with a 

 brush transfer the selected filaments to a watch-glass or 

 saucer of water. With scissors cut these filaments into 

 pieces which can be covered by a cover-glass, and mount 

 them in water. 



With the low power, select a suitable filament, move the 

 slide so that this filament crosses the centre of the field, 

 put on the high power, and study carefully the appearances 

 successively presented by the cell- walls and cell-contents 



Fig. 56. SPIROGYRA. Part of a Filament, showing the Structure of 

 one of the Cells. 



on focussing with the fine adjustment, beginning with the 

 upper surface and turning the micrometer screw until the 

 middle is reached (giving an " optical section " of the cell) 

 and finally the lower surface. Sketch a portion of the 

 filament, including at least one complete cell, as seen (a) 

 in upper surface view, (6) in optical section. Note 



(1) The outer or longitudinal cell-wall, smooth and 

 colourless and often covered by a layer of mucilage. 



(2) The disc-like transverse walls, continuous with 

 the outer wall and dividing the filament into a row of 

 cylindrical cells. 



(3) The thin continuous film (" primordial utricle ") of 

 colourless fine-grained protoplasm lying within the cell- 

 wall. 



(4) Embedded in this film and running spirally round 

 the cell, the green band-like chromatophore there may 

 be several chromatophores in each cell. 



