176 THE STRUCTURE OF FLOWERS. 



Camellia become striped; while ammonia enhances the 

 colours of Balsams. 



Oxidization is believed to have great inflaence in chang- 

 ing the colours of plants, just as it affects certain juices when 

 exposed to the air. Thus, if a leaf of the Socotrine Aloe be 

 injured, the juice is at first violet in tint, but it soon turns 

 to brown. If a potato be grated, the pulp rapidly browns in a 

 similar way. Many fungi, especially noted for their poison- 

 ous properties, turn blue on injury, as species of Boletus. 

 Moreover, they do not do so if exposed to nitrogen, hydrogen, 

 or carbonic acid; hence it is presumably the oxygen which 

 effects the change. 



Some flowers change their colours from their first open- 

 ing to a full expansion : such as Cobcea, from green to violet; 

 several Boraginaceous plants, from red or even yellow to blue- 

 purple. Lycium harbarum, the popularly called " Tea-plant,'* 

 is a well-known instance. Others change during the day, as 

 the " Changeable Hibiscus.'^ This plant has flowers white 

 in the morning, pink at noon, and bright red by sundown.* 

 Similarly, a Phlox of a bright pink colour, " in the early morn- 

 ing, by five o'clock, has its colour of a lightish blue, which 

 continues to alter as the sun advances, and by nine or ten 

 o'clock becomes its proper colour ; the clump which catches 

 the sun's rays first changes first, while the other is still blue." 



Though referring these and other well-known instances to 

 oxidization. Dr. Lindley, from whose leading article the above 

 remarks are partly taken, concludes with the observation, 

 " In fact, we know very little about the cause of changes in 

 colour, either in plants or animals." Perhaps it remains so 

 still. 



The intensity of the colours of many high Alpine flowers 



* According to M. Ramon de la Sagra; quoted in Gard. Chron., 1842, 

 p. 555. 



