SEAWEEDS AND THEIR ALLIES. 101 



salt solution is suitable for this purpose. Watch 

 the process of plasmolysis (contraction of the proto- 

 plasm and its separation from the cell-membrane). 

 Sketch one or two of the cells showing the cell- 

 membrane in its place and the contracted proto- 

 plasmic contents. 



Preparing a fresh slide, so as to have the cells in 

 their natural condition, study the cell-contents. 

 How many green bands, chlorophyll bodies, are 

 there in each cell ? Change the focus slowly, and 

 follow a band from one end of the cell to the 

 other. What is its shape? Is its edge even or 

 irregular? Notice the rounded, highly refractive 

 bodies, pyrenoids, contained in it. 



Treat with iodine solution, and ascertain whether 

 starch occurs in the cells. If so, does it stand 

 in any relation to the pyrenoids ? 



Look for a nucleus. This is sometimes brought out 

 very plainly by the action of iodine. In some 

 species it may be seen with perfect clearness with- 

 out any treatment. Compare different specimens 

 until you know definitely 

 a. The position of the nucleus in the cell. 

 I. Its shape. 



0. Whether it is connected in any way with other 

 parts of the protoplasmic contents. This is a 

 very interesting point, difficult to determine in 

 some species, but very obvious in others. 

 d. Its structure. A nucleolus will readily be found. 

 (The finer details of structure require special 

 methods not provided for in this course.) 



