503 



substances in the leaf cell that the chlorophyll used in the formation of the 

 chlorophyllan is constantly and quickly replaced by the preponderant process 

 of assimilation, in which case usually no yellow coloration of the chlorophyll 

 body is noticeable, or the chlorophyll body may be protected by a substance 

 which does not let the acid through, gradually losing this protection in the 

 autumn. However, both processes might take pace and, according to the 

 above experiments, this is most probable. 



Frank and Wiesner refer to the actual presence of an arrangement in 

 the chloroplasts which protects them against the attacks of the acid cell sap. 

 They emphasize that the green grains lie imbedded in protoplasm which is 

 impervious to acids. Tschirch has also mentioned that each chlorophyll 

 grain is surrounded by a colorless cytoplasmic membrane (hyaloplasma- 

 layer) which is especially easily proved in water plants, and in this way 

 possesses a special protection against the acid cell sap. 



As the leaf cell approaches the end of its life in the autumn the proto- 

 plasm is no longer ver}^ abundantly present. But even where it is still more 

 abundant, it undergoes, in the cold of the autumn, a change (which may be 

 overcome by heat), making it permeable to acids. Frank found that the 

 yellow coloration, produced by the action of acid on the chloroplasts, had 

 already occurred when they, together with the nucleus, lay closely imbedded 

 in the cytoplasmic wall layer. Such a change in the diosmotic character- 

 istics of the protoplasm of evergreen trees also makes possible the action of 

 acids. The organic acids increase, however, in the autumnal leaf in this 

 way, making easier leaf coloration. 



In regard to the red coloration, C. Kraus^ has proved that the Brenz- 

 catechin (orthodihydroxbenzine) first found by Gorup-Besanez- in wood- 

 bine occurs in all leaves which change color in the autumn even (so far as 

 the partial investigation extended) in all leaves still growing vigorously. 

 This substance turns green with ferric chlorid and a beautiful red with vege- 

 table acids. The extracts of the leaves give the reactions of oxyphen acid, 

 on which account the conclusion is pertinent that the red coloring matter in 

 the young leaves and in those which have changed color in the autumn 

 comes from the increased effect of the Brenz catechin, due to the increased 

 action of the acid. 



Summarizing all that has been said previously we can consider the 

 process of the autumnal change of color as a process of oxidation, increased 

 in proportion to the process of assimilation and due to the effect of light. 



This acts very differently on the substances present in the cells of the 

 various plants, so that the chlorophyllan is produced from the chlorophyll 

 coloring matter and the leaf becomes yellow\'' If the Brenz catechin, 

 which may be produced artificially from carbo-hydrates and probably is 



1 t)ber die Herbstfarbung der Blatter und die Bildung- der Pflanzensauren. 

 Biedermanns Centralbl. 1874, I, p. 126. 



2 Annalen der Chemie und Pharmacie 1872, Vol. CLXI, Parts 2 and 3. 



3 The chlorophyllan extraction of leaves dead in the autumn shows the same 

 "bandes accidentelles permanentes" as Chantard emphasized earlier (Centralbl. f. 

 Agrikulturchemic 1874, p. 40). 



