386 RELATIOy TO ENVIRONMENT, 



The red and purple colors are found suffused in the cell-sap of certain 

 cells in the leaf much as we have found it in the cells of the red beet. The 

 yellow color is chiefly due to the disappearance and degeneration of the 

 chlorophyll whik^ the leaf is in a moribund state. A similar [phenomenon 

 is seen in the yellowing of crops when the soil becomes too wet, or in the 

 blanching of grass when covered with a board, or of celery as the earth 

 is ridged up ovct the leaves in late summer and autumn. A number of 

 different theories have been advanced to explain autumn coloring, i.e., 

 the appearance of the red coloring-matter. It has bt-en attributed to the 

 approach of cold weather, and this has likely led to the erroneous behei 

 on the part of some that it is caused bv frost. It very often precedes frost, 

 Some have attributed it to the action of the more oblique light rays during 

 autumn, and still others to the diminishing watcr-supplv with the approach 

 of cool weather. The question is one whirh has not met as ^'Ct ^^"ith a 

 satisfactory soluticjn, and is certainlv a \'(t^' ol iscnre onr. It is likclv 

 that the low temperature or the declining activities of the leaf affect certain 

 organic substances in the leaf and give rise to the rod color, and it is quit^ 

 certain that in some years the display is more brilliant than in others. 

 The color is nnjre striking in some regions than in others a]id the differem 

 soil, as well as climate, has been su])posed to ha^e some inlluence. The 

 North American forests are noted for the l.irilHant display of autumnal 

 color. This is perhaps due to some extent Uy the great variety or number 

 of species which display (olor. It would seem that there is some specitic 

 as well as individual ]>e( uliarilies in c<Ttain trees. Some individuals, 

 for example, exhibit brilliant colors ever\- autumn, while others near of 

 the same species are more subdueil. 



It has been shown by experiment tliat when sunhght ])asses through 

 red colors the temjierature is slighlh' inen-ased, and it has been suggested 

 that this may be of protection to the living sul.)stance whii. h has ceased 

 working and is in danger of injury from cold. ThcTe does not seem to 

 be much ground for this suggestion, howe\-er. It certainb' coukl not 

 protect the protoplasm of the leaf at niglit when the col.l is more intense, 

 and during the day w<juld only aggra\'ale matters by supplying an in- 

 creased amount of heat, since extremes of heat and cold in alternation 

 are more harmful to plant life than uniform cold. ICspeeiallv would this 

 be the case in alpine climates where the ;ilternation of heat and cold be- 

 tween day and night is extreme, and brillianev of the colors of alpine plants 

 is well known. It seems more reasonable to suppose that tiie red color 

 acts as a screen, as the chloroph\ll is disappearing, to protect from the 

 injurious action of light, certain organic substances which are to be trans- 

 ferred liack from the leaf to the stem for winter storage. So in tlie rase 

 ol many stems in ihe spring or v:\\\\ summer when llie \'oung leaves often 

 have a reddish ( ulor, it is likely that it acts as a screen to protect the liviu'^ 



