18 ASSIMILATION. [CH. II 



from intercellular air. They are then placed in methyl- 

 ated spirit warmed to 50°-60° C. : cold spirit will remove 

 the chlorophyll equally well but not so quickly : if the 

 specimens are not wanted at once the best results will be 

 obtained by putting them in the sun for a few hours. 

 The preliminary boiling in water must on no account be 

 omitted, it shortens the process of decolorising in the 

 most remarkable manner ; of this it is easy to convince 

 oneself by trying, for instance, to decolorise an Entero- 

 morpha without the hot-water treatment. To produce 

 the iodine reaction place the decolorised leaves in 

 alcoholic tincture of iodine diluted with water ^ to the 

 colour of dark beer. In a few minutes they will be 

 stained, and after washing in fresh water, they should be 

 spread out on a white plate so that their tint — by which 

 the amount of starch is roughly gauged — may be well 

 seen. When full of starch they are almost black, and 

 with less amounts of starch the colour sinks through 

 purple, grey, and greenish grey to the yellow tint of 

 starchless leaves. 



(25) Schimper's method^. 



In some cases it is necessary to use the microscope, 

 this is especially necessary when the amount of starch 

 present is small, or where, as in Schimper's researches, 

 the distribution of starch in the leaf is particularly 

 studied. 



Prepare a strong solution of chloral hydrate by dis- 

 solving the crystals in as much distilled water as will just 



1 Spring water answers perfectly well. 

 " Bot. Zeitung, 1885. 



