1871.] Various Tints of Autumnal Foliage. 71 



altered into the browner modification, and then its produc- 

 tion merely gives rise to a dark brown which does not attract 

 the eye. The deep brown colour of heath in autumn is an 

 example of this, and on careful examination it may be seen 

 that the brown shade is almost entirely confined to the side 

 of the plant which is exposed to strong light. The red 

 colouring matter is so disguised by the green chlorophyll 

 that one would scarcely expect to extract, by the method 

 already described, a colour quite equal in beauty to carmine, 

 and of almost exactly the same tint. Very many other 

 illustrations might be given of the same general fact, but 

 the colour does not attract attention until the chlorophyll 

 fades, and then the mixture of the previously existing red 

 with a more or less pure yellow gives rise to scarlet. This 

 may be seen to great advantage in the leaves of the common 

 bramble and many other plants. It may then be asked why 

 we never see a fine scarlet in the case of heath or purple 

 beech. The explanation seems to be that in them the red 

 colour is not the same as in the case of the numerous plants 

 which turn scarlet, and is so much more easily decomposed 

 that it entirely fades before the chlorophyll is altered. The 

 spectrum method indicates that the colour of these two 

 plants is the same, but differs from that red colour which 

 occurs in most of those turning to a fine scarlet, as, for 

 example, in the leaves of the bilberry, bramble, hawthorn, 

 Berberis, cherry, apple, and guelder-rose. In other plants 

 the red colour is not specially developed, whilst the 

 chlorophyll is unchanged, but is produced at the time of that 

 change, as if in some way dependent on the same cause. 

 I have especially studied this point in the case of the leaves 

 of the common sorrel, and find that the production of the 

 red colour depends in some way on exposure to light, and on 

 loss of perfect vitality. I had long known that most of the 

 bright red leaves met with in the fields were those which 

 had been broken off from the plant, and yet when dried in 

 the house, or even kept in the dark with their stalks in water, 

 the green leaves fade to dull yellow. I therefore placed in 

 my garden detached leaves with their stalks in the earth, 

 some with the upper, and some with the lower surfaces 

 exposed to the light, some in the sun, and some in the shade, 

 and I found that those which turned to a fine red were those 

 exposed to the sun with the lower surface upwards. I have 

 also noticed that the red colour is often produced in spots 

 where the leaf has been injured by insects ; and in the case 

 of other plants I have remarked that the leaves on partially 

 broken twigs show this colour to unusual advantage. I am 



