THE FOOD OF PLANTS. 21 



So-called crude chlorophyll solutions we can ultimately obtain 

 from any green plant structures ; but in order to get a relatively 

 pure extract, it is suitable to employ young wheat plants, or 

 Elodea plants. We cut off the aerial parts of young wheat plants 

 which have developed, say, six leaves, or we collect a moderate 

 quantity of fresh Elodea plants, place the material (say 100-150 

 gr. of fresh substance) in a porcelain dish, and boil it for some 

 time (55 hour) with distilled water on the water-bath. The 

 liquor is poured off, the residue is washed several times with 

 distilled water, and then, after being squeezed, is treated in a large 

 flask with J to 1 litre of 95 per cent, alcohol. The extraction 

 proceeds pretty quickly, especially if we gently warm the flask. 

 It is necessary to prepare the extract in the dark, since chloro- 

 phyll, as we shall see later, is very readily decomposed under the 

 influence of light. The solution obtained has a splendid green 

 colour. 



Chlorophyll, as associated in the plant cells with a protoplasmic 

 matrix, must on no account be regarded as a single chemical 

 individual ; it is a mixture of two pigments, yellow xanthophyll 

 and blue-green cyanophyll, as we may readily prove by the 

 following experiment. 



Into a glass cylinder we pour a very concentrated alcoholic 

 solution of chlorophyll, add water drop by drop, but not sufficient 

 to produce any turbidity, treat with benzol, shake well, and let 

 stand. The mixture rapidly separates into a lower alcoholic 

 golden yellow solution of xanthophyll, and an upper blue-green 

 solution of cyanophyll in benzol. The yellow pigment is more 

 readily soluble in alcohol than in benzol, the blue-green one more 

 readily soluble in benzol than in alcohol, and hence the separation 

 of the two pigments. 



In the cells of plant structures grown in the dark, and there- 

 fore yellow in colour, occur large quantities of etiolin grains 

 (see 10). These consist of a protoplasmic matrix and a yellow 

 pigment, which we can isolate by extracting with alcohol wheat 

 or barley seedlings, e.g., etiolated by growth in the dark. The 

 extract has a beautiful yellow colour. We obtain the necessary 

 plant material by sowing soaked wheat or barley grains on moist 

 sawdust, and cultivating the young seedlings for about eight days 

 in the dark. 



1 G. Kraus, Zur Kenntniss der Chloropliyllfarbstoffe. Stuttgart, 1872. 



