December 15, 1916] 



SCIENCE 



857 



course possible that the two kinds of chlorosis 

 may be found to be essentially the same except 

 for certain secondary effects produced by an 

 undue absorption of manganese. 



P. L. GlLB 



Porto Rico Age. Exp. Sta., 

 Mayaguez, Porto Eico 



RELATIVE IMPORTANCE OF FUNGI AND 

 BACTERIA IN SOIL 



To the Editor of Science : In a recent 

 number of Science, 1 Waksman discusses the 

 question : " Do Fungi Live and Produce Myce- 

 lium in Soil ? " He answers the question in 

 the affirmative. I have been interested in the 

 same question for some time and have arrived 

 at conclusions slightly different from those 

 to be inferred from Waksman's article. 



Waksman has tested for the presence of 

 mycelium by placing a lump of soil about 1 

 cm. in diameter in the center of a plate of agar 

 (containing Czapek's solution 2 for nutrient 

 material). After 24 hours at 20-22° C, he 

 finds that mold hyphas radiate out into the 

 medium from this lump of soil. If instead 

 of soil he uses a drop of water in which mold 

 spores are suspended, the amount of mycelium 

 produced in 24 hours is very much smaller. 

 From these findings he concludes that such 

 a lump of soil contains living mycelium. 



This conclusion is undoubtedly supported by 

 theoretical considerations. The soil is con- 

 tinually showered with mold conidia from the 

 air and without question contains moisture 

 enough to allow them to germinate even if 

 conditions are not favorable for their long- 

 continued growth. The presence of mush- 

 rooms, moreover, in woodland soil and even 

 in fields and lawns, proves beyond doubt that 

 conditions do favor the growth of certain 

 Basidiomycetes, at least. Their mycelium un- 

 doubtedly penetrates the soil sufficiently to be 

 present in a lump as large as that used by 

 Waksman. The question of real importance, 



i Science, N. S., 44, pp. 320-322. 



2 Waksman does not publish the formula of this 

 solution, but it has been obtained from him in a 

 personal letter. It is : MgS0 4 0.5 g., E^HPO, 1 g., 

 KC1 0.5 g., PeS0 4 0.01 g., NaNO„ 2 g., Sucrose 

 30 g., to one liter of water. 



however, is whether the mycelium is abundant 

 enough in the soil to compare in its activ- 

 ities with the soil bacteria. Waksman does not 

 discuss this question; although from his state- 

 ment that the plate method gives figures as 

 high as 1,000,000 fungi per gram soil, the 

 natural implication is that they must be 

 nearly as important as bacteria. His actual 

 data, however, show nothing of the sort. He 

 merely shows that mold hypha? can be found 

 in lumps of soil 1 cm. in diameter. A lump 

 of soil that size contains many millions of 

 bacteria. Compared to their activities, those 

 of a few mold hypha3 would be quite insig- 

 nificant. 



I have tested several soils by Waksman's 

 method, and have generally obtained results 

 similar to his; but because the information 

 furnished by it is not quantitative, I have 

 modified the method by the use of smaller 

 quantities of soil (crumbs weighing about 10 

 mg.), with quite different results. Such a 

 crumb of soil should contain, according to the 

 plate method — which is generally acknowl- 

 edged to give figures that are much too low — 

 perhaps 100,000 bacteria. If fungi are of any- 

 thing like the same importance as bacteria in 

 soil, one of these crumbs should certainly con- 

 tain mold hypha?. Their presence, however, 

 has been indicated only in the case of soil to 

 which large amounts of organic matter (ma- 

 nure or grass roots) have been added. When 

 crumbs of soil to which no organic matter has 

 been added have been used, the development 

 of mold hypha? in the agar has been slower 

 than in the case of drops of water containing 

 nothing but mold conidia. This certainly 

 suggests that no mycelium is present in these 

 small crumbs and that molds are relatively 

 insignificant in soil; but as the crumbs of soil 

 were always surrounded at the end of 24 hours 

 by vigorously growing bacteria, it is possible 

 that the development of mold hyphse may have 

 been suppressed. For this reason, Waksman's 

 method is considered inconclusive. 



It seems as if the question could be con- 

 clusively answered only by the use of a micro- 

 scope. The microscope would furnish direct 

 instead of presumptive evidence on the sub- 



