104 



SCIENCE 



[N. S. Vol. XLI. No. 1046 



favors tlie digestion of starch and the trans- 

 location of carbohydrates, and especially that 

 it increases the activity of the starch-digesting 

 enzyme. Wortmann disagreed with this, but 

 Stahl, in his researches with variegated leaves, 

 found a satisfactory explanation of the favor- 

 able inifluence of the red pigment on the proc- 

 ess of the translocation of materials. The 

 formation of red pigment in leaves in spring 

 and fall, and in high mountains, in summer, is 

 associated with low temperatures which retard 

 the translocation of the photosynthate, and 

 thus decrease the activity of photosynthesis. 

 Stahl's thermoelectric investigations with red- 

 spotted leaves demonstrated an increased ab- 

 sorption of heat in those parts of the leaves 

 containing anthocyan. On the basis of these 

 results, Stahl modified Pick's thesis as follows : 



In the heat-absorbing red coloring matter of 

 leaves the plant possesses a medium, for accelera- 

 ting the transformation of matter and energy. 



Contrary to the light-shield theory, which 

 holds that the anthocyan is a protection against 

 the destructive effect of a too intensive light 

 on the chlorophyll, Stahl's theory, especially 

 in view of the favoring of the process of trans- 

 location, has the advantage of either giving 

 biological significance to the red pigment in 

 autumn leaves, or of pointing the way to in- 

 vestigations of the metabolism in autumn-red 

 leaves. 



It remains to be proved whether the favor- 

 ing influence of the red pigment on the trans- 

 location of material may actually be demon- 

 strated by comparative chemical analyses, or, 

 in other words, whether and in how far red 

 leaves, under the same conditions, suffer a 

 more thorough emptying out than do other 

 leaves on the same plant which have not formed 

 the red pigment. Swartz's analyses of green, 

 yellow and red leaves of Parottia persica, with 

 reference to nitrogenous contents showed that, 

 before leaf-fall, the red leaves are more thor- 

 oughly emptied than the yellow ones. 



If a leaf is dropped from the branch shortly 

 after its color has turned (be the color either 

 yellow, red or white) the cells still remain 

 alive, except in a few cases where pari passu 



with the loss of chlorophyll a brown pigment 

 spreads over the leaf-surface. The outer ap- 

 pearance and also the microscopical characters 

 indicate that the cells by no means contain 

 merely disorganized matter, but maintain their 

 complete vital functions until the appearance 

 of the brown and black color, which indicates 

 the death of the leaf. Thus, with Tswett, 

 Swart concludes that the color change of leaves 

 is not a postmortem decomposition, but a phys- 

 iological process, and that we have to distin- 

 guish two phases in the change of color, viz., 

 the necrobiotic, with its yellow, red and white 

 tints, and the postmortem, characterized by 

 the appearance of brown and black color. 



But Swart holds that the theory of trans- 

 location does not stand and fall with the ques- 

 tion as to whether the leaf during yellowing 

 becomes dead or not, for, as he has shown in 

 the investigations here recorded, the trans- 

 location of material still takes place from the 

 portions of leaves that have already entered 

 upon change in color. Nevertheless, Swart 

 adds, the theory, in consideration of certain 

 cases, must suffer a certain limitation. 



A chapter on final considerations (pp. 97— 

 117) concludes the book. 



0. Stuart Gagee 



SPECIAL ARTICLES 



ON THE ORIGIN OF THE LOESS OF SOUTHWESTERN 

 INDIANA 1 



The gallant defenders of the grand old 

 aqueous theory of loess deposition seem to be 

 retreating southward, though their rear-guard 

 vigorously contests every district yielded. Just 

 now they seem to be crossing the Ohio River. 

 Humor has it that a strip on the north side 

 of the river in southwestern Ohio is still being 

 claimed; southwestern Indiana^ has been in 

 their undisputed possession for 10 years; and 

 the latest publications on the geology of west- 

 ern Kentucky and southeastern Missouri con- 

 tain such words as " the writer may state his 



1 Published hy permission of the Director of 

 the United States Geological Survey. 



2 Bull. Geol. Soo. Am., Vol. 14, pp. 153-176 and 

 the Patoka folio TJ. S. Geol. Survey. 



