FUNCTION OF ACTINOMYCETES IN SOIL 199 



This complexity in the group and the confusion in nomen- 

 clature, however, must not hide the fact that an Actinomyces 

 causes potato scab, nor that Beijerinck, approaching the sub- 

 ject from an entirely different angle, has shown them to be 

 associated with the roots of other plants. It is also to be re- 

 membered that Actinomycetes are thought to be concerned in 

 the decomposition of organic matter. Some recent observa- 

 tions at the New York Experiment Station bear on this point. 



In the course of a qualitative study of the bacteria in certain 

 New York State soils, it was early recognized that there was a 

 great similarity between different soils in the relative numbers 

 of Actinomycetes and lower bacteria present, provided the soils 

 were in the same state of cultivation. Later it also became 

 evident that the Actinomycetes were practically always present 

 in greater abundance in old sod soil than in soil recently cul- 

 tivated. This difference is shown in Table I, in which the num- 

 bers of Actinomycetes found in 20 samples of various sod soils 

 are compared with the numbers occurring in an equal number 

 of samples of cultivated soil. Although it is possible to pick 

 out numerous cases in which the number occurring in some 

 one of the cultivated samples is greater than in some of the 

 sod samples, nevertheless the average number in sod soil is 

 twice that in the cultivated soil. The table also shows that 

 the Actinomycetes averaged 39.4 per cent of the total flora of 

 sod soil, but only 21.3 per cent of the flora of cultivated soil. 

 There is only one instance (October 22, 1913) in which the 

 percentage of these organisms in sod soil is as low as their aver- 

 age percentage in cultivated soil, and only one (January 4, 1911) 

 in which their percentage in cultivated soil is as high as their 

 average percentage in sod soil. 



These figures furnish a strong indication that Actinomycetes 

 are more numerous in sod than in cultivated soil; but even be- 

 fore all the data given in Table I were collected the importance 

 of making a more satisfactory comparison was realized. To 

 do this, a study was made of a considerable variety of soil types,' 



^ The soil nomenclature of the Bureau of Soils has been used in this work. 

 The soils mentioned are described in the Soil Surveys of Ontario and Tomp- 

 kins Counties, New York, published by this Bureau. 



