SOCIETY OF CENTRAL ILLINOIS. 185 



THE RELATION OF SOIL ORGANISMS TO THE GERMINA- 

 TION AND GROWTH OF PLANTS. 



BY PROF. S. W. PARR, JACKSONVILLE. 



The problem of plant nutrition, and the conditions essential to 

 growth are matters of very great practical importance. 



We have arrived at our present state of knowledge of such 

 things by slow and uncertain steps — chiefly the result of hard ex- 

 perience. But in these later days, the scientist has taken the plant 

 into the laboratory and greenhouse and studied it chemically, biolog- 

 ically, bacterially. And the indications are that we are about to 

 step into and possess a new field of information; one that almost 

 startles us with its size and value, because of the possibility of be- 

 ing better able to interpret and apply our hard-earned, and not al- 

 ways well-understood experience. 



In the first place, then, for a fuller understanding of what is to 

 follow, let us recall a few facts concerning plant food and nutrition. 



The two sources of food supply are the air and soil. In gen- 

 eral, we may say that the plant, if we were to burn it, would in that 

 process give up to the air those elements it received from the air as 

 food — while in the ashes would remain those food elements it re- 

 ceives from the suil. Among these latter we have to deal, at present 

 with one only, and that is Nitrogen — an essential element, and 

 without which no plant could live. Moreover, this nitrogen, besides 

 being taken up by the roots can only be utilized by them when in 

 a nitraie form, as we find it in such salts as nitre, or calcium, or 

 ammonium nitrate. En other words, the nitrogen, combined as it is 

 in undecayed vegetable, or albuminous matter, or in form of ammonia 

 — no matter how abundant, can in no degree be utilized by the plant 

 as food. Now, the question arises, what is the source of supply of this 

 nitrate form of plant food? Any of these nitrate salts are highly solu- 

 ble and are being constantly leached out of the soil so that there must 

 be some constantly renewed cource of supply. Theories on this point 

 are numerous. Four-fifths of the atmosphere is pure nitrogen — 

 but not in the plant-food condition. Unquestionably the electrical 

 discharges during thunder-storms serves to oxidize some nitrogen 

 which is thus carried down by the rain within reach of the plant 

 roots. 



But this supply is but a minute fraction of the demand; so we 

 are obliged to look elsewhere for the source of our nitrates, without 

 stopping to discuss the numerous theories which have remained — 

 sim[)ly theories for lack of possibility of proof. Let us turn at once 

 to aiheory which seems about to step into the realm of accepted 

 fact, because of the frequent demonstration it seems to receive. 



The theory has been proposed by Schloesing and Muntz, and 

 later by Warrington, of the Rothamstead Farm, England, and is 



