GEEEN COLOUR OF PLANTS. 



391 



respect, 1 being the highest value, 

 effect was not satisfactorily tested :- 



The sign — indicates that the 



Ex. Plants. 



1. Turnips. 



2. Beans . 



3. Turnips. 



4. Turnips . 

 6. Turnips. 

 6. Turnips . 



Hours of 

 sunshine. 

 . 22 

 . 14 

 . 8- 

 . 23 

 . 17-5 

 . 5-5 



Total 

 time. 



109 

 95 

 69 



101 



52 



The ray producing the green colour is found to be that which acts 

 most efficiently in the decomposition of carbonic acid, as shown by 

 the following table : — 



The green colour becomes lighter or deeper according to the 

 quantity of chlorophyll and the aggregation of the cells. It is usually 

 paler on the lower sides of leaves. The dark shades of green in the 

 Yew, Bay, and HoUy, are the effect of an immense crowding together 

 of green cells. 



As light decreases in autumn, the chlorophyll, in many cases, 

 diminishes, and is probably altered by the loss of a portion of carbon. 

 Thus, Evergreen leaves become of'a paler colour, and deciduous leaves 

 assume various hues, commonly called autimmal tints. The leaves of 

 the Poplar, Ash, and Beech, before faUing, become yeUow; those of 

 some species of Khus, bright red; those of Oomus sanguinea, dull 

 red ; those of the Vine, yellow and purple. Berzelius states that the 

 leaves become red in plants having red fruits. Eobinet and Guibourt 

 maintain that the Vines which produce bluish grapes have red leaves 

 in autumn, while such as produce white grapes have yellow leaves. 

 These yeUow and red colours by some are said to depend on changes 

 in the state of oxidation of" the chlorophyll, and have been traced by 

 others to the production of peculiar substances, one red, called eryth/ro- 

 phyll, the other yellow, xanthophyll. Marquaxt believes that the action 

 of water on chlorophyll, in different proportions, gives rise to yellow 

 and blue matters. Ellis supposed the change of hues to be due to 

 the prevalence of acid and alkaline matters. 



Mai-tens says that the colour of chlorophyll depends on the mix- 

 ture of anthocyane, blue colouring (xvavog, blue), and anthoxanthine, 

 yellow colouring {^avSog, yellow). Chlorophyll has a tendency to 



