44 PRACTICAL BOTANY 



advantage of simplicity, stain the sections from material 

 hardened in alcohol, with a solution of methyl green 

 in weak acetic acid, wash with weak acetic acid, and 

 mount in dilute glycerine : the nucleus only is distinctly 

 stained in this case, but the results are as a whole less 

 satisfactory than when the former method is used. 



In the sections above described numerous examples of dividing 

 nuclei will be found, especially if the material be fixed imme- 

 diately after being cut, and if the plants had been previously 

 kept at a high temperature. For further details of the course of 

 nuclear and cell division see below. 



III. Starch. 



a. Scrape the freshly-cut surface of a Potato tuber 

 lightly with a knife, and mount a small quantity of 

 the scrapings in water : examine first with a low, and 

 then under a high power, and observe scattered through 

 the water a large number of somewhat ovoid, colourless, 

 bright-looking, i.e. highly refractive bodies : these are 

 starch-grains ; near to one end, which is usually 

 slightly pointed, is a round clear spot, the hilum. The 

 grain will show a stratified structure : the layers of 

 stratification near the hilum are almost circular and 

 concentric ; the more external layers are excentric and 

 elliptical, and are wider on the side further from the 

 hilum ; many of them between the hilum and the 

 broader end of the grain are incomplete ; hence the 

 layers are more numerous between the hilum and the 

 broad end than between the hilum and the pointed end 

 of the grain. 



Here and there may be seen a compound grain, 

 consisting of two small grains in contact by their 



