Ill THE COLOURS AND PIGMENTS OF PLANTS 63 



tion from the brightly coloured leaves of some species 

 of Coleus. He found, however, that on boiling these 

 leaves with water, he did not obtain a coloured 

 solution, although the leaves themselves lost their 

 colour. If, however, the colourless solution be 

 evaporated to dryness, anthocyan is left behind in 

 its blue or violet form. Similarly if the decolorised 

 leaves be dried at a gentle heat they regain their 

 bright colours. The reason for this remarkable 

 phenomenon Molisch found to be as follows. Dur- 

 ing life the cell-sap in these coloured leaves is faintly 

 acid or neutral in reaction, but the protoplasm is as 

 usual distinctly alkaline. At the moment of death 

 the alkaline protoplasm mingles with the cell-sap, 

 and the alkalinity of the protoplasm is strong enough 

 to completely destroy the anthocyan colour (cf action 

 of alkalies as explained above). Molisch also found 

 that leaves which are not decolorised on boiling are 

 remarkable for the large amount of acid contained 

 in the cell-sap, this being apparently large enough to 

 neutralise the alkalinity of the protoplasm. By 

 further experimentation Molisch convinced himself 

 that the decolorisation only occurred when the cells 

 containing anthocyan were in contact with cells very 

 rich in chlorophyll. This he illustrated by a very 

 pretty experiment. He took the leaves of a species 

 of Saxifrage, Saxifraga sarmentosa, in which the epi- 

 dermal cells of the leaf are very rich in anthocyan, 

 and removed a small part of the epidermis from 

 a leaf. Both the piece of epidermis and the re- 

 mainder of the leaf were then kept at a temperature 

 sufficient to kill the cells, and so bring the cell-sap 

 into contact with the protoplasm. In a quarter of 



