November 8, 1912] 



SCIENCE 



613 



tion before we can have a true explanation 

 of why some crops are benefited by the 

 so-called sterilization of some soils. 



Aside from a very few pathogenic forms, 

 but little is specifically known of the fun- 

 gus flora of the earth. That fungi may be 

 as abundant as the bacteria, particularly 

 in uncultivated soils and that below the 

 humus-containing layer, they may consid- 

 erably exceed the bacteria, has been ascer- 

 tained by a few analyses. But what they 

 do and how they do it, is for the most part 

 a matter of conjecture. To those fa,miliar 

 with the rapidity and certainty with which 

 some of the higher fungi reduce organic to 

 inorganic matter, it is evident that there 

 is no group of organisms present in the 

 soil that would seem to be more capable of 

 producing profound changes in its environ- 

 ment. Not only do we know that a con- 

 siderable amount of the decay in animal 

 and vegetable tissue, particularly the early 

 stages, is due to the higher fungi, but the 

 work of Czapek and Kohn, showing that 

 Penicillium and Aspergillus when supplied 

 with ammonium chloride set free hydro- 

 chloric acid, as well as the demonstration 

 of the production of an organic acid in 

 Penicillium by Alsberg and Black, points 

 to still further possibilities by plants be- 

 longing to the same, or closely related 

 groups. 



Formerly it was supposed that the num- 

 ber of plants whose roots entered into com- 

 bination with some fungus — presumably 

 for mutual benefit — ^was limited and con- 

 fined to but few families. Now it is esti- 

 mated that about one half of the seed 

 plants possess within their roots some 

 mycorhizal organism and in many notable 

 instances the plant is unable to thrive 

 under natural conditions without its par- 

 ticular fungus. Furthermore, as has been 

 pointed out by Coville, the acidity factor 

 in the distribution of some plants is myco- 

 logical rather than purely chemical. 



Our knowledge of the effect of soil fungi 

 upon the germination of seed is also being 

 extended. Barnard has recently shown 

 that seed of both the common potato and 

 Solanum dulcamara fail to germinate in 

 the absence of their mycorhizal parasite, 

 while 40-90 per cent, begin to grow in the 

 presence of this fungus. 



Whether the considerable number of 

 wild yeast-like organisms occurring abun- 

 dantly in many soils, are capable of pro- 

 ducing profound changes in their habitat 

 is still problematical. That certain of 

 these may fix atmospheric nitrogen in the 

 laboratory seems to have been demon- 

 strated, and it appears reasonable that 

 should conditions in the earth be favorable, 

 we might expect yeasts to have a decided 

 effect either upon the soil, or its inhabit- 

 ants. Despite the necessity of yeasts hav- 

 ing secondary breeding places, such as 

 aqueous extracts from fruits and other 

 vegetable matter, the soil must be consid- 

 ered the chief abode of these fungi, and 

 not only during the colder months, but 

 throughout the entire year. 



Even less is known about the algal con- 

 tent of the soil than of its fungus constitu- 

 ents. The older literature is full of refer- 

 ences to the nitrogen-fixing power of both 

 grass-greens and blue-greens, but it is a 

 striking fact that since the introduction of 

 the pure culture method for algse, there 

 has been no authenticated demonstration 

 of the power of these plants to add in the 

 slightest degree to our store of fijsed nitro- 

 gen. It is true that Heinze working with 

 impure cultures of Nostoc thought he had 

 demonstrated by a process of elimination 

 its ability to fix nitrogen. Since Azoto- 

 iacter was not present and the fungus in 

 the culture could not by itself fix nitrogen, 

 he assumed that the nitrogen accumulated 

 must be due to the alga. But this can 

 hardly be accepted as conclusive. "While it 

 it possible that some of the blue-greens 



