SPIROGYKA. 89 



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. 



&. The green spiral chromatophores (one or more), 

 embedded in the membrane : 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, attaching 

 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 Algae. Look for examples illustrating their 

 multiplication by fission. In material decolorised in alcohol, or 

 fixed by some other method, apply such staining reagents as 

 hsernatoxylin and carmine : the pyrenoids will stain in a manner 

 similar to nuclei. 



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

 observed in the filaments of Spirogyra ; the chief 

 difficulty is however that the process normally takes 

 place at night, beginning about 10 to 12 P.M. Stras- 

 burger, who has made this a subject of careful 



