The Life of the Fly 



of the reason. Both of them turn blue, with 

 an admixture of green. A third species, the 

 bluish boletus (Boletus cyancscens, BULL., 

 var. lacteus, LEVEILLE), possess remarkable 

 colour- sensitiveness. Bruise it ever so lightly, 

 no matter where, on the cap, the stem, the 

 tubes of the under-surface : forthwith, the 

 wounded part, originally a pure white, is 

 tinted a beautiful blue. Place this boletus in 

 an atmosphere of carbonic acid gas. We can 

 now knock it, crush it, reduce it to pulp; and 

 the blue no longer shows. But extract a frag- 

 ment from the crushed mass : immediately, at 

 the first contact with the air, the matter turns 

 a most glorious blue. It reminds us of a pro- 

 cess employed in dyeing. The indigo of com- 

 merce, steeped in water containing lime and 

 sulphate of iron, or copperas, is deprived of a 

 part of its oxygen; it loses its colour and be- 

 comes soluble in water, as it was in the original 

 indigo-plant, before the treatment which the 

 plant underwent. A colourless liquid results. 

 Expose a drop of this liquid to the air. 

 Straightway, oxidization works upon the pro- 

 duct : the indigo is reformed, insoluble and 

 blue. 



This is exactly what we see in the boleti that 

 turn blue so readily. Could they, in fact, con- 



412 



