Application of the Micro-spectroscope, &c. By Thos. Palmer. 235 
viously existing chlorophyll, I do not think we shall err much 
from the path of truthful inquiry. 
A natural question arises however ; is not the chlorophyll in 
such instances as these actually dependent on the red colouring 
matter ? Or, more simply speaking, is it not actually in existence 
when the leaf is still green ? So far as my experience goes, I 
certainly should answer these questions in the affirmative, for I 
have known these red leaves to turn green again as summer has 
approached ; still there is a difference in the red which denotes the 
declining scale to that which is the effect of a season, and I there- 
fore cannot help thinking but that it is in some measure due to 
temperature ; when that falls, the equilibrium between the con- 
structive and destructive agencies is so much modified by the 
reduction of vital activity exerted on the part of the plant itself 
that the amount of chlorophyll formed is considerably less in 
proportion to that of the red substance which exists as a rounded 
hyaline strongly refractive mass in the upper part of the palisade 
cells, and appears sometimes as red, sometimes as yellow, and con- 
sists mainly of tannin, while the chlorophyll grains intact and of a 
beautiful green are all crowded together in the inner end of these 
cells, whereas in the more seasonable weather of spring and summer 
the reverse is occasioned, and consequently the leaves assume their 
natural colour — green. 
The fact that other plants of the evergreen order do not turn 
red appears to me to be analogous to the state in which the 
chlorophyll exists in them. Laurel and holly, for example, do not 
turn red in winter ; still there is very little doubt but that their 
leaves become darker as the temperature falls, and this I am rather 
disposed to attribute to the action of a blue or brown compound 
which acts in exactly the same way, though it is not so noticeable 
as in the case last enumerated. 
The spectra which I have recorded are taken first, as in Fig. 8, 
from the leaves in a mature state ; second, as in Fig. 9, from the 
young ones ; and third, as in Fig. 1 0, from those which have 
assumed a red hue. 
Fig. 8.— Mature Leaves of Arbutus. 
M. 
Observations. 
1 
22-00 
Centre 
649-0 
Class 1. Very black ; size -4. 
2 
22-76 
594-5 
„ 2. „ dark; size -27. 
3 
20-05 
» • • 
532-5 | 
„ 1. Shaded, centre dark ; size 
•30. 
4 
1 19-00 
>1 
498-0 | 
„ 1. Shaded, centre dark ; size 
•6. 
| 19-5 
Commencement 
482-5 
General absorption ; black. 
