Mat 12, 1911] 



SCIENCE 



743 



ing the humus available. Saida^ has shown 

 that the parasitic fungus Phoma heiw can fix 

 nitrogen in the presence of cane sugar, as 

 follows : 



Cane sugar 



Cane sugar 



Cane sugar (4-(NHj2C03 trace) 

 Cane sugar ( + (NHJ2C03 trace) 

 Cane sugar ( + (NH4)2C03 trace) 

 Cane sugar (-f-CNHJoCOj trace) 



ligrams 



.7393 



1.1828 

 1.1828 

 1.7742 

 3.5484 

 6.2097 



'More recently Ternetz* has isolated five 

 endophytic mycorhizal fungi from certain 

 Ericacese, all of which have been found to 

 belong to the genus Phoma. Three of these 

 organisms, Phoma radicis oxycocci, Phoma 

 radicis vaccinii and Phoma radicis andro- 

 medw, have shown a well-developed capacity 

 for nitrogen fixation in culture, these three 

 mentioned working even more economically 

 than Azotohacter chroococcum, the amount 

 of nitrogen fixation in milligrams per gram of 

 dextrose being under the conditions of culture, 

 respectively 22.14, 18.08, 10.92 and 10.66 for 

 the four organisms mentioned. 



With these discoveries in view, we can 

 briefly summarize. The starch in fallen 

 autumn leaves is converted by certain forest 

 soil bacteria into glucose. This glucose is 

 utilized directly by the roots of forest trees, 

 by various saprophytic plants and by the my- 

 corhiza, which by the aid of the glucose are 

 enabled to fix considerable amounts of nitro- 

 gen. That the soil is the seat of other activi- 

 ties of as much importance to growing plants, 

 as the above, is proved by the presence of the 

 nitrifying and denitrifying bacteria, of the 

 bacteria that produce the root nodules of the 

 Leguminosse, of such organisms as Clostridium 

 pastorianum, Bacillus mycoides, B. ellen- 

 hachensis, Azotohacter chroococcum, A. Vine- 



° " Ueber Assimilation freien Stiekstoffs dureh 

 Schimmelpilze," Ber. d. deuisoh Bat. Ges., 19: 

 107-115, 1901. 



* Duggar, B. M., " Fungous Diseases of Plants," 

 p. 74; Ternetz, Charlotte, "Ueber die Assimila- 

 tion des atmosphilrisehen Stickstoffes durch 

 Pilze," Jahrb. f. iviss. Bat., 44: 353-408. 



landii and the hyphffi of numerous saprophy- 

 tic fungi, various putrefactive bacteria, which 

 perform their role in making the soil the fit 

 habitation of the higher flowering plants, pro- 

 ducing the tilth or " Bodengare " of the 

 Germans. So too earthworms, insect larvae, 

 ants and burrowing animals assist in the 

 task of aerating and mixing the surface layers 

 of the soil. It is also evident that the produc- 

 tion of toxic excretions by the roots of plants 

 is undoubtedly a factor of importance in soil 

 fertility. Following out a clue which the par- 

 tial sterilization of the soil by chemicals or 

 by steam gave, it was discovered that the 

 bacteria which are useful in ammonia- 

 making increased four-fold after such treat- 

 ment, suggesting the presence in the soil of 

 some agent which held them in check. After 

 much painstaking study, it was discovered" 

 that the soil contained a living protozoon 

 {Pleurotricha) , which preyed upon the useful 

 organisms, and that the heat and chemicals 

 either destroyed these larger unicellular ani- 

 mals', or inhibited their activity. It can be 

 said, therefore, that the fertility of the soil 

 is largely a biological one, as well as depend- 

 ent upon the physical, chemical and toxic con- 

 dition of the surface layers. That the produc- 

 tivity of some soils is due to biological rather 

 than to physical and chemical characteristics 

 is illustrated by the attempts made to reforest 

 Denmark. The peninsula of Jutland was 

 covered originally by forests, but these were 

 destroyed, until by the year 1500 the country 

 had been transformed into a barren heath and 

 sand dunes. At various times attempts were 

 made to reforest these heaths but the results 

 were disappointing until Col. E. Delgar' solved 

 the problem. Spruce trees (Picea alba, P. 

 excelsa), if planted alone did not thrive, but 

 became sickly. The cause of this irregularity 

 in the growth of spruce was thought to be 

 local conditions of the soil, but scientific in- 

 vestigation of such soils did not reveal any 



"Hall, A. D., "The Soil as a Battleground," 

 Harper's Magazine, October, 1910, pp. 680-687. 



° Hovgaard, William, " The Reforestation of 

 Denmark," American Forestry, XVI., 525-529, 

 September, 1910. 



