22 ASSIMILATION. [CH. II 



and free from intercellular air. They are then placed 

 in alcohol warmed to 50 60 C. : cold alcohol 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 

 jEnteromorpha without the hot- water treatment. To 

 produce the iodine reaction, place the decolorised leaves 

 in alcoholic tincture of iodine diluted with water 1 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) Schimpers method 2 . 



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 minutely 

 studied. 



Prepare a strong solution of chloral hydrate by dis- 



1 It is not necessary to use distilled water. 



2 Hot. Zeitung, 1885. 



