Morning journal and courier., 1885-01-07
The AutumnaI T1nts of Foliage.

I
 After the fine display of autumnal tints
 which we have lately seen it may, I trust, be l of interest to some of the readers of Nature
 if give all account of the chief conclusions l to which I have been led by carefully study. | ing the subject for'many years.
 As a general rule the color of leaves in their normal condition depends variable
 mixture of two perfectly distinct green pig
 ments and of at least four perfectly distinct yellow substances. The development of the l autumnal tints is mainly due to the disap- pearance or change of the green constituents | and to the production of highly colored pig ments by the oxidization of previously exist | ing very pale or colorless substances. It is, | in fact, due to a more or less complete loss of the vitality which previously enumerated these chemical changes, and the order ill which the tints are developed can be easily explained, if we assume that the death of the leaves takes place somewhat gradually. The first visible effect of the reduced vitality is the change in the green pigments. In many cases they appear to be converted into color less products, since the resulting bright vel low leaves differ from the normal green in
 the absence of chlorophyll, and merely con tain the usual previously existing yellow pig ments. At the same time it is quite possi- ble that increased quantity of some of these yellow substances may be formed as a product during the change, but of this there is no positive proof. In the case of such
 trees as the alder the chlorophyn does not thus disappear, but is changed by the pres, ence of q week acid into very stable brown ish-green product which resists further change. The production of bright yellows or dull browns thus clearly depends on l whether the chIorophyll does or does net dis Ioco of acids, as may be verified experimentally by exposing suitable solutions to sunlight. 1t is, however, very clear that the manner in which it changes depends very much on the conditions of the case. Thus if chlorophyll is exposed to sunlight dissolved in bisulphide of carbon, a reddish-colored product is formed, and though this differs very greatly
 from the red pigment met with in many au-
 tumnal leaves, it seems probable that under
 some conditions the chlorophyll in leaves is
 changed by the action of light into 8 red
 substance By taking green sorrel leaves
 and keeping them somewhat fresh by stick
 ing the stalks into moist ground I found
 that those exposed to the sun with the under
 side upward turned to bright red whereas
 those kept in the shade did not develop any
 fine coloring. We may often see that par
 tially broken leaves or twigs undergo this
 change when all other parts of the tree
 main green and this and various other facts
 lead me to conclude that the change of chlor-
 ophyll into red product depends on cer-
 tain amount of reduced vitality well on
 little-understood conditions varying in diff
 ferent kinds of plants. Though 1 fully ad-
 init that there are some facts not easy to un-
 derstand yet on the whole it seems to mo
 that these principles fairly well explain why
 certain leaves turn red in autumn. Slight
 frosts reduce their vitality in such manner
 that the chlorophyll is changed by the ac-
 ton of the light into a red product. Thus,
 according to the character of the season and
 the nature of the plants, the first effect of
 the reduced vitality in the leaves is that the
 chlorophy1l is removed so as to show their
 normal yellow color or is changed into red
 pigment, or is altered into n comparatively
 stable dull l-brown green product These are
 the three extreme changes, but in many cases
 intermediate mixed results give rise to such
 less perfect and wel-1narked tlnts h dirty
 yellOws and reds.
 The next series of changes is best studied in the case of those leaves which in the first instance turn to Il bright yellow, and it ap- pears to ine that they depend mainly, if not entirely, on the production of deeply colored pigments by the oxidi2ntion of tnnnic acid and other more or loss cUorless substances. The difference in the resulting tint serins to depend on tho nature of these substances Thus, for example, the tainic acid in the yellow oak leaves changes into a brown substance, whereas the qtiiuotniihic acid in ytltDW btttit leaves tlhiigeS lltU thS Htlt Dfaiige bfbwi color which makes these trees sD ornamental in autumn. On the contra ty, the bright yellow poplar leaves rapidly
 LASS tU t dafk, dirty bfuWi bt lhe alteia iluif If another tbhstilHBiit Other kinds If leaves eiFp fisr t6 tlnts uf ai iHtefine1i ate and iess Hei marked character. tR many Gasgs It Ia aiiaoat impossible tu draw the line between the pgeF if this stage ii the change and the final dark and diFE browns If dead and deeaFlHg leaves: FGF | HHe effect FeFF much depends HpaH th | production af each special tint in 2 fairly | pure state, SD as te shaW bright yeileWs, | reds and browns. This seems to be iniH= | enead by the character of the weather. It | is also, of caHFse, important that the halt dead leaves should hang long on the trees, so to develop their full coloring before | being blown off by the wind
 Taking thus all the facts into considera ton, it appears clear that all the bright and beautiful tints of autumn are merely | the earliest stages of decomposition, and are due to the more or less considerable triumph of chemical forces over the weak aned or destroyed vitality of the living plant. One cannot but feel that this is a very unpoetical way in which to regard he magnificent tints of fine autumnal but it is no less true than that he colored clouds of evening mark the de- parting day.