CELLS IN LOWER PLANTS. 



91 



a. Eacli cell will undergo a partial plasmolysls (see Fig. 7-, 3). 



j3. The nucleus, and especially the nucleolus, will turn brOWn 

 (reaction for proteid). 



y. The pyrenoidS are acted upon as follows : — The central portions 

 may stain a yelloioish-hrown, whilst the outer parts turn blue. This 

 reaction shows that starch is present at the periphery of the pyrenoid. 



Under a high power of the microscope it is possible to study 

 the pyrenoids more closely. It will then be found that some of 

 these bodies are completely surrounded by a ring of starch, 

 whilst others have only a few separate granules arranged round 

 them in the form of a circle (see Fig. 72, 2). 



Fig. 72.— 1. A Single Cell from a Filament or Spiroijyra. Note the 

 delicate layer of peripheral cytoplasm, the nucleus held in the middle 

 of the cell by strands or bridles of protoplasm. The spirally wound 

 chlorophyll band has numerous pyrenoids arranged in line along its 

 axial portion. 



2. PoKTioN or THE CHLOROPHYLL Band after the cell has been 

 treated with iodine solution. The uppermost pyrenoid has a ring of 

 small separate starch-granules round it ; the lower one is completely 

 surrounded by a ring of starch. 



3. Plasmolysis in a Cell or Spirogyra. Bridles of protoplasm 

 pass at first from the plasmolysed portion to the cell-wall. 



