108 COLOUR, TASTE, ODOUR. 



lutions of Acetate of Lead and Sulphate of Ammonia, 

 whilst I made use of Sulphate of Iron and Ferro Cya- 

 nate of Potassa. In these experiments it will be seen 

 that materials were employed which react upon each 

 other in minute quantities ; the plants impregnated 

 with one or other of these substances, were placed to- 

 gether in a glass of pure water, but neither Unger nor 

 myself ever saw a separation of the absorbed matter by 

 the unhurt radicles, but which happened in my own 

 experiments as soon as they were cut." 



138. The last point we may notice, is that in many 

 plants the excretion of water takes on a material form 

 either in particular organs like the pitchers of Nepen- 

 thes, or Cephalotus, or at once upon different parts of 

 the surface of the leaf ; and it is stated that water has 

 been known to fall as a light rain from the leaves of 

 Poplars and Willows in shady places when the weather 

 was hot and serene, and the same thing from Caesal- 

 pinia pluviosa, has been observed in the Brazils. 



COLOUR, TAST3, AND ODOUE. 



139. Colour. The mode in which plants receive their 

 colour is in three ways ; the most general is that whilst 

 the membrane of the structure is transparent, its cellules 

 are filled with a colourless fluid in which the coloured 

 globules are contained, which by shining through the 

 membrane, give rise to the colour ; the second, that 

 whilst the membrane, is still transparent and colourless, 

 the fluid contained in it is coloured; the third, and 

 least common, is that the membrane itself is coloured. 



140. It was soon remarked that the general colour of 

 plants, green, was very much altered in its tint accord- 

 ing to the degree of light to which the plants were sub- 

 jected, that when they were grown in a somewhat dark 

 place, they got paler, and if nearly all light was exclu- 



