98 



ORGANS AND FUNCTIONS OF PLANTS. 



of producing a coloured precipitate within the plant, 

 by means of two colourless chemical solutions. With 

 this view he watered a plant of Bigonia discolor with 

 a solution of the cyanuret of potass and iron, and 

 afterwards with a solution of sulphate of the oxide of 

 iron, when a blue precipitate was produced by these 

 two solutions meeting together within the plant in the 

 tube of what appears from his figure copied below 

 to be a spiral vessel, and called by him an air tube. 

 No colour was found in the roots.' 



A, the cellular tissue; B, the vessel coloured blue by the 

 precipitate. 



M. Bischoffof Bonn, finding that the interior of a 

 plant was very irregularly and uncertainly coloured in 

 such experiments, discovered that coloured liquids are 

 only sucked up when the air is absent, and he found 

 he could cause the colour to ascend at pleasure, by boil- 

 ing the coloured water, or otherwise abstracting the 

 air, and the contrary. 



