444 PRACTICAL BOTANY 



3. The protoplasmic body, which consists of 



a. A colourless membrane (primordial utricle) 



which lines the cell-wall internally, and surrounds the 

 large central vacuole. 



b. The green spiral chromatophores (one or more) 

 embedded in the protoplasm : note their irregular out- 

 line, and the numerous highly refractive lenticular bodies 

 (pyrenoids) which are contained in them. 



c. A. bi-convex lens-shaped nucleus, suspended in 

 the centre of the vacuole by fine colourless strands of 

 protoplasm, which run to the primordial utricle, attach- 

 ing themselves to points opposite the pyrenoids. 



Stain with an iodine solution, and observe that the 

 colourless protoplasm stains pale yellow, the nucleus a 

 deeper yellow, and it will thus be more clearly seen, as 

 well as one or sometimes two nucleoli which are 

 deeply stained : the pyrenoids stain a dusky purple. 



A careful comparison of these pyrenoids under high powers, 

 with and without iodine staining, will lead to the conclusion that 

 they are highly refractive, colourless bodies, around which is 

 usually present a coating of starch, either as a continuous sheath, 

 or in distinct granules. Such bodies are to be found in the chro- 

 matophores of many Algee. Look for examples illustrating their 

 multiplication by fission. In material decolorised in alcohol, or 

 fixed by some other method, apply such staining reagents as 

 hsematoxylin and carmine : the pyrenoids will stain in a manner 

 similar to nuclei. But the best method for bringing out clearly 

 the structure of the pyrenoids is that of fixing and staining with 

 picro-nigrosin (see Appendix A) : after staining wash in alcohol 

 and mount in weak glycerine : both the nuclei and the pyrenoids 

 will be stained, while the starch-sheath remains colourless. 



II. The process of cell-division may be very well 

 observed in the filaments of Spirogyra ; the chief 



