100 



SCIENCE 



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



tree. By this act the metabolism of the re- 

 maining leaves is known to be altered. Thus, 

 for example, the rapidity of the translocation 

 of carbohydrates from leaves is increased with 

 the diminution of the number of leaves on the 

 plant; by partial defoliation transpiration 

 from the remaining leaf surfaces is increased, 

 and this is accompanied by a more rapid de- 

 pletion of starch. The taking in of the nu- 

 trient salts is also favored by a diminution in 

 the number of leaves. 



If dead leaves are used in the analysis, 

 another source of error is introduced, since 

 substances may be washed out of dead leaves 

 exposed to the weather. In former researches 

 a yellow color has been held to indicate death, 

 and all yellow leaves accordingly designated 

 as dead. Swart discusses these, and other 

 sources of error in all researches on the subject 

 prior to Wehmer's Kriiik of 1892. He argues 

 with Wehmer that all results published before 

 his paper can be relied upon to only a limited 

 extent, but he disagrees (p. 37) with Weh- 

 mer's view that these results argue against the 

 validity- of the theory of a depletion before 

 leaf-fall, for he knows of no case where the 

 failure of a translocation has been demon- 

 strated beyond doubt. 



In his own researches Swart employed the 

 method devised by Stahl, of cutting out, with 

 a die (or a cork-borer), portions of the leaves 

 for analysis, thus avoiding the troublesome 

 and inaccurate measuring of the area of an 

 entire leaf. Tabular statements of the results 

 of several analyses are given on pages 59 to 

 67, the material including leaves of Anthurium, 

 sp., Liriodendron Tulipifera, Ginho hiloia, 

 Laserpitium latifolium, Parothia persica, 

 2Eschylus Hippocastarmm, Salix caprwa, 8or- 

 hus intermedia, Quercus sp., and others. These 

 analyses show that the leaves in the brief pe- 

 riod preceding their fall and during their col- 

 oring, had suffered a loss of nitrogen, phos- 

 phoric acid and potassium, and these losses, 

 especially in the case of nitrogen and phos- 

 phoric acid, were quite considerable. These 

 results confirm in toto those of former investi- 

 gators. The slight loss of magnesia in indi- 

 vidual cases may, in the opinion of the author, 



be attributed to variations in the analyses, in 

 consequence of the inequality of the research 

 material. Iron remains rather constant. 



It is worthy of note that calcium, silica, 

 phosphoric acid and chlorine, materials which 

 at other times become richer in leaves, increase 

 only a little, or not at all. From this it may 

 be inferred that, in general, in the last vital 

 period of leaves, only slight additional quanti- 

 ties of nutrient salts are taken in from the soil. 

 On the other hand, the two analyses of Laser- 

 pitium (as shown in the table, page 67), in so 

 far as they are comparable, indicate that the 

 composition of leaves may vary considerably 

 in different years. 



No general law or principle can be formu- 

 lated from the knovsm behavior of nitrogen, 

 phosphoric acid and calcium. Such an infer- 

 ence must be based on a study of all the in- 

 vestigations bearing on the subject. The fact 

 that the literature contains certain contradic- 

 tions as to the behavior of calcium, serves only 

 to indicate (in so far as the researches have 

 been carried out with sufficient care) that the 

 behavior of any given substance is not uniform, 

 but varies, within wide limits, according to 

 the plant and the external conditions. 



In consideration of the rather considerable 

 losses, especially of nitrogen and phosphoric 

 acid, suffered by the leaves studied by Swart, 

 he finds himself in entire agreement with the 

 view for which Eamann and Stahl contend, 

 namely, that the loss of substances suffered by 

 leaves before their fall is wholly restricted to 

 their period of yellowing. Microscopic in- 

 vestigations of yellowed leaves (pages 70-96) 

 also substantiate this conclusion. 



The second chapter is devoted to The Color- 

 ing of Leaves. Having demonstrated that the 

 translocation of nutrient materials, resulting 

 in a permanent loss of these substances from 

 the leaves, takes place in the relatively short 

 period of a few weeks' duration, marked exter- 

 nally by the loss of chlorophyll, the author 

 now turns his attention to this period, in order 

 to ascertain how far a study of the yellowing 

 of leaves would lead to the same conclusions as 

 did the chemical analyses. 



The period of yellowing or of coloring in 



