28 PRACTICAL BOTANY 



3. That each cell contains a protoplasmic body, 



the most marked part of which will be one or more 

 spiral chromatophores, coloured bright green by 

 chlorophyll. 



In order to study the structure of the protoplasmic 

 body in detail, put on a high power, and make the fol- 

 lowing observations of the filament, which, it is to be 

 remembered, is in the living condition : 



1. Having recognized the smooth colourless cell-wall, 

 note that it is closely invested internally by 



2. A continuous film of colourless protoplasm (the 

 " primordial utricle "), of which the external layer 

 (ectoplasm) is more transparent than the granular 

 internal layer (endoplasm). 



3. That this protoplasmic film surrounds a large 

 central cavity the vacuole filled with perfectly 

 transparent cell-sap. 



4. That in the peripheral film are embedded 

 one or more green spiral bodies (chromatophores) 

 of flattened form, and very irregular margin, each in- 

 cluding numerous lenticular, highly refractive bodies, 

 the pyrenoids. 



5. Focussing carefully downwards into the central 

 cavity, a highly refractive, colourless, lens-shaped body 

 is to be seen suspended in a central position by 

 numerous finely granular protoplasmic threads : this 

 body is the nucleus. 



a. These several points should be made out in the 

 living cell, without treatment with any reagent ; but 

 their observation may be made easier in various ways. 

 Irrigate (p. 15) with iodine solution, and observe the 

 following results of that treatment : 



