742 



SCIENCE 



[N. S. Vol. XXXIII. No. 854 



tion has pointed the way along which future 

 research on soils must proceed and some of 

 this instructive work may be reviewed here 

 briefly and in a sequence which suggests the 

 orderly manner in which effect follows cause. 

 Harter* in a paper entitled the " Starch 

 Content of Leaves dropped in Autumn " has 

 shown that the well-established belief that 

 autumn leaves contain very little carbohydrate 

 in the form of starch and sugar is erroneous, 

 for during the summer of 1909, he undertook 

 to trace the change taking place in the amount 

 of starch formed in the leaves of Liquid- 

 ambar styraciflua at different periods, viz., 

 August 17, September 15, October 23 and 

 October 28. On October 28, the leaves were 

 collected which had fallen recently from the 

 tree. The starch in the leaves collected at the 

 different dates was determined quantitatively 

 and was found to be as follows: August 17, 

 10.91 per cent.; September 15, 10.33 per cent. ; 

 October 23, 11.47 per cent, and October 28, 

 10.79 per cent., based on the dry weight of the 

 material. Since so much starch was found in 

 the fallen leaves of the sweet gum similar ma- 

 terial was collected from several other plants 

 and the starch determined as above. The 

 amount of substances in the leaves capable of 

 reducing the copper in Fehling's solution, as 

 determined by the above method, are shown 

 in the table: 



Per Cent 



Liquidambar styra<n-flna 10.79 



Gingko biloba 6.32 



Platanus ori&ntalis 11.84 



Platanus occidentalis 9.89 



Styrax americana 5.91 



Magnolia obovata 7.19 



Quercus pedunculata 14.54 



Elceagnus umbellata 10.24 



The thought suggested to me after reading 

 the results of Harter's work was one which 

 considered the final disposition of the starch 

 in the fallen leaves. Is this starch disin- 

 tegrated, or is it changed into a form by 

 which it can be utilized by the roots of forest 

 plants and by the organisms of the soil? To 



^The Plant World, 13: 144-147, June, 1910. 



answer this question, I would call attention 

 to the studies of a graduate student of mine, 

 who in a recent piece of work on " Bacteria 

 and other Fungi in Eelation to the Soil " has 

 discovered the ultimate destiny of this carbo- 

 hydrate material. Dr. Eivas^ by a detailed 

 analysis of the bacterial content of virgin 

 forest soils has shown that the largest num- 

 ber of bacteria are found during October, 

 and the least number during the winter 

 months. He finds that the forest soils con- 

 tain bacteria which produce enzymes capable 

 of fermenting the carbohydrates, as shown 

 in the following tabulation of his results, 

 which shows the relative proportion of the 

 different ferments produced by the species 

 isolated. 



Per 

 Cent. 



1. Diastatic ferment acting on starch, found 



in 24 cultures 60.0 



2. Inverting ferments, inverting starch or 



saccharose into glucose found in 29 cul- 

 tures 72.5 



(A) Inverting starch into glucose found 



in 22 cultures 55.0 



(B) Inverting saccharose into glucose 



found in 14 cultures 35.5 



The presence of these organisms in the soil 

 clearly points to the fact not previously con- 

 sidered in the study of forest soils, that the 

 starch found in autumn leaves can be con- 

 verted directly by such soil organisms into 

 glucose, and it is probable that this sugar is 

 directly absorbed by the roots of higher plants 

 (a fact not previously suspected), either by 

 the root hairs, or by means of the mycorhiza 

 found abundantly on the roots of many forest 

 trees. Such sugar is also utilized by non- 

 chlorophylless plants, saprophytic fungi (Agar- 

 icus), and flowering plants (Monotropa), for 

 it has long been known these plants can absorb 

 the whole of their organic food (including the 

 soluble carbohydrates) from the humus and 

 that the various mycorhiza living in commen- 

 salism with the roots of phanerogams are 

 probably of considerable importance in render- 



- " Contributions from the Botanical Labora- 

 tory of the University of Pennsylvania," III., 

 243-274. 



