267 



(5) The edges of the chromatophore are usually serrated, 

 while along the middle there is a series of conspicuous 

 rounded bodies, each consisting of a central pyrenoid 

 surrounded by small strongly refractive starch-grains. 



(6) The large central cell-cavity or vacuole, containing 

 the colourless cell-sap. 



(7) The nucleus, a strongly refractive body, usually 

 lens-shaped, lying in the centre of the cell and surrounded 

 by a layer of protoplasm from which proceed fine radiating 

 protoplasmic threads. 



381. Cell treated with Iodine. Treat filaments with 

 iodine either remove the cover-glass, add a drop of 

 iodine, and mount in water after washing off the super- 

 fluous iodine with water, or irrigate with iodine and then 

 with water and compare with fresh filaments. Note that 

 the starch- masses around the pyrenoids are stained dusky 

 purple or almost black ; the protoplasmic contents are 

 stained brown; the nucleus is more deeply stained than 

 the general protoplasm, and the nucleolus contained in 

 the nucleus still more deeply ; the threads radiating from 

 the protoplasm around the nucleus are branched, and may 

 be traced outwards to the pyrenoids close to which they end. 



382. Decolorised Cells. Place some filaments in alcohol (strong 

 methylated) ; the chlorophyll is dissolved out of the chromatophores 

 and the alcohol becomes green. Rinse a decolorised filament in 

 water, treat with iodine, and note that the starch and protein 

 contents are stained as in fresh material ; the chromatophores are 

 seen to be specialised band-like portions of the protoplasm. 



To see the pyrenoids clearly, decolorise and treat with iodine 

 filaments that have been kept in shade or darkness until starch- 

 free. To stain the cell-wall as well as the cell-contents, either use 

 alcohol material, or filaments preserved in formalin ; or (better) 

 place fresh material in 400 c.c. of water with 1 gram chromic acid 

 and 4 c.c. glacial acetic acid, leave in this fixing solution overnight, 

 then wash by steeping in water for a few hours (changing the water 

 two or three times), and stain with safranin or haematoxylin or 

 aniline blue, or safranin followed by one of the other stains. 



383. Flasmolysis. Alcohol and various other reagents cause 

 the cell-contents to separate more or less completely from the cell- 

 wall, leaving a space between the protoplasm film and the wall. In 

 this state the cell is plasmolysed ; alcohol, iodine, etc., not only 



