342 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1913. 



various kinds of coal were deposited they may safely hypothesize 

 that the purer coals were laid down in waters that were acid. 



Allusion has been made to the peculiar characteristics of plants 

 that inhabit peat. Among these peculiarities perhaps none is more 

 remarkable than the presence of mycorhizal fungi on the roots of 

 many, perhaps most, peat-loving plants. It is known that peat is 

 very poorly supplied with nitrogen in the form of nitrates, which 

 most plants of alkaline soils appear to require. Organic nitrogen, 

 however, is abundant in peat, and there is very strong evidence that 

 these mycorhizal fungi take up this organic nitrogen, and probably 

 atmospheric nitrogen also, and transfer it in some acceptable form 

 to the plants in whose roots they live. Unfortunately, the work of 

 botanists on these fungi has been confined largely to the determina- 

 tion of the mere anatomical fact of their occurrence on the roots or 

 in certain of the root cells, with descriptions of their size and con- 

 figuration. Little attention has been paid to the isolation of the 

 fungi, their culture and identification, or to the demonstration of 

 their physiological action. The only hypothesis, however, that satis- 

 factorily explains what we already know about the mycorhizal fungi 

 is that the,y prevent the nitrogen starvation of peat-inhabiting plants. 

 It is well known that certain peat-bog plants, as, for example, sundew 

 {Drosera)^ trap insects, digest them, and assimilate their nitrogen. 

 It is to be hoped that within a few years we shall be equally well 

 informed about the function of the mycorhizal fungi. But even now 

 we may speak of their probable function with confidence. 



The mycorhizal fungi are known to occur on most of the trees that 

 inhabit acid situations, for example, chestnut, beech, oaks, and coni- 

 fers. The ordinary hillside pasture in New England is a mycorhizal 

 cosmos. The club mosses have them, the sweet fern (Comptonia), 

 the blueberries, the ferns, the orchids. In our sandy pine and oak 

 woods about Washington almost all the vegetation possesses myco- 

 rhizal fungi. One comes to think of the giant oaks as dependent on 

 these minute organisms. 



Were Solomon to write a new edition of the Proverbs to-day I am 

 sure that he would tell us " There be four things which are little 

 upon the earth, but they are exceeding strong," and that among the 

 four he would include "The little brothers of the forest, they seek 

 not the light but the leafy earth; they prepare for the oak the 

 strength that is his." 



Our American agi'iculture, derived in the main front the agricul- 

 ture of the ISIediterranean region, and that in turn from the older 

 agriculture of Persia, is chiefly made up of plants that thrive best in 

 alkaline or neutral soils. Although many of our soils in the eastern 

 United States are naturally acid, we try with only indifferent success 

 to grow in them these alkaline plants of southern Europe and the 



