August 24, 1917] 



SCIENCE 



173 



bers to be important compared with bac- 

 teria. There seem to be two questions in- 

 volved here : How large a proportion of the 

 number of molds developing on plates rep- 

 resent active forms and how many spores? 

 What is the number of active mold forms 

 which need be present in the soil for them 

 to be considered important in the various 

 soil chemical processes ? 



The first of these questions is rather diffi- 

 cult to answer at the present time, but our 

 experiments indicate that rather a large 

 proportion of the total number of molds 

 present in various soils occur in the active 

 state. We have found active mold growth 

 occurring in all the soils thus far examined, 

 and we have used both Waksman's and 

 Conn's methods. Our results confirm 

 Waksman's observations, therefore, and 

 Conn's criticism seems unwarranted, for 

 active mold mycelia have developed in all 

 our tests, using not only 10 mgs. but also 

 smaller quantities of soils, as well as the 

 larger lumps employed by Waksman. The 

 soils tested are normal soils, many of them 

 untreated and none extremely rich in 

 humus. 



Further work along this line is certainly 

 desirable, but from our observations thus 

 far there seems no doubt but that fungi 

 occur actively in soils, and hence we feel 

 that their action must be important regard- 

 less of their relative numbers compared 

 with bacteria. Furthermore the presence 

 of spores is likewise important for they 

 may become active in the near future and 

 bring about their characteristic reac- 

 tions. The answer to the second ques- 

 tion mentioned above can only come 

 after long-continued experiments, but from 

 the vigorous action of molds noted in so 

 many cases, as will be pointed out later, it is 

 evident that the problem of microorganic 

 activity in relation to soil fertility can not 

 be completely solved without a knowledge 



of mold growth. Perhaps they are not as 

 important as bacteria, there is no means yet 

 of knowing, but even if of secondary signifi- 

 cance they deserve recognition. Our pres- 

 ent knowledge of soil fertility is too incom- 

 plete to permit us to pass over hastily any 

 possibly important factors without thor- 

 ough study. 



We believe, therefore, that molds occur 

 in most soils, both in the active and in the 

 spore state, and hence they must pass 

 through their various life cycles in the soil. 

 Furthermore, difi'erent soils undoubtedly 

 have different fungus floras. Species pres- 

 ent under one combination of conditions 

 may be absent under others. Organisms 

 present only as spores in one case may occur 

 actively in other instances. Finally, it 

 seems perfectly possible that the relative 

 occurrence of active and spore forms of va- 

 rious organisms may vary in the same soil 

 with varj'ing conditions of moisture, tem- 

 perature, aeration, reaction and food 

 supply. 



Considering the occurrence of molds in 

 an active state in all soils an established 

 fact, the importance of these organisms in 

 the decomposition of the soil organic mat- 

 ter becomes evident. Many experiments 

 have been conducted along this line and it 

 has been very clearly demonstrated that 

 molds ai'e very efficient ammonifiers. Indi- 

 cations have been secured that there exists 

 a correlation between the biological stage 

 of the organisms and the periods of am- 

 monia accumulation. The largest amount 

 seems to accompany the periods of spore 

 germination and the smallest amount the 

 time preparatoi'y to actual spore formation. 



All the nitrogenous organic materials 

 which make up the humus content of soils 

 are easily attacked by various fungus forms 

 and ammonia is liberated in large amounts. 

 Part of this ammonia may, of course, be 

 utilized by them, but by far the larger part 



