GREEN COLOUR OF PLANTS. 325 



on the subject, by making the light pass through coloured media, and 

 he was led to the conclusion, that while the yellow rays had the 

 greatest effect on the growth of the plant, the blue and chemical rays 

 were those chiefly concerned in the production of the green colour. 

 Hunt seems to agree with Senebier. Other experimenters, however, 

 as Morren, Daubeny, Draper, and Gardner, think the yellow rays are 

 the most active in producing the green colour. The following table 

 shows the result of some of Gardner's experiments. The rays are 

 denominated active or inactive in relation to their power of producing 

 a green colour, and the figures under each of them show their power 

 in this respect, 1 being the highest value. The sign indicates that 

 the effect was not satisfactorily tested : 



T? PI nf Hours of Total. Active rays. Inactive. 



sunshine. time. Red. Or. Yel. Gr. Bl. In. Vio. 



1. Turnips 22 ... 109 .. 4 2 1 3 .. 



2. Beans 14 ... 95 ... 2 1 3 .. 



3. Turnips 8 ... 69 ... 4 2 1 3 .. 



4. Turnips 23 ... 101 ...__ 1 .. 



5. Turnips 175 ... 52 ... 2 1 3 .. 4 



6. Turnips 5'5 ... 6 ... 4 2 1 3 . 



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

 acts most efficiently on the decomposition of carbonic acid, as shown 

 by the following table : 



Places of spectrum Production of Decomp. of Illuminating 



examined. chlorophylle. CO 2. power. 



Extreme Red 0-000 0-0000 .. 00000 



Commencement of Urange '5500 .. 



Centre of Orange '777 .. 



Centre of Yellow 1-000 1-0000 .. I'OOOO 



Centre of Green, -583 . .. 



Centre of Blue, -100 .. 



674. The green colour becomes lighter or deeper according to the 

 quantity of chlorophylle 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 Holly, are the effect of an immense crowding together 

 of green cells. 



675. As light decreases in Autumn, the chlorophylle, 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 autumnal tints. The leaves of 

 the Poplar, Ash, and Beech, before falling, become yellow ; those of 

 some species of Rhus, bright red ; those of Cornus sanguinea, dull red ; 

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

 become red in plants having red fruits. Robinet and Guibourt main- 

 tain that the Vines which produce bluish grapes, have red leaves 



