THE SOIL AND ITS EFFECT ON PLANT GROWTH. 15 



mthout regard to its possible economic worth, and also of the 

 way in which two scientists, working independently, may in due 

 course come together and combine their results into a successful 

 weapon of attack on a difficult problem. 



A research worker at Rothamsted was endeavouring to find 

 means of artificially rotting straw. He discovered that there 

 were certain kinds of bacteria present in straw, and in the soil, 

 which had the power of absorbing free nitrogen from the air, and 

 that through the agency of these organisms, wetted straw gradually 

 became richer in nitrogen. The organisms were isolated, and an 

 attempt was made to see if .their power of using free nitrogen 

 could not by some means be augmented, so that the fertilising 

 value of the straw could be increased through the activity of 

 these so-called " nitrogen-assimilating bacteria." But the 

 attempt was not entirely successful. The bacteria could absorb 

 nitrogen only up to a certain point, and at this stage the straw 

 was still of little value as a direct fertiliser. Simultaneously with 

 this work, however, research was going on in another department 

 of the Institute, the object being to discover the organisms 

 which are able to decompose cellulose. The Rothamsted worker 

 was successful in discovering and isolating an organism capable 

 of effecting cellulose decomposition. Its life history was worked 

 out, and it was found that fixed nitrogen — i.e. nitrogen in the 

 form of a compound — of some kind or another, was essential for 

 its growth. Now straw contains a large proportion of cellulose, 

 and at this stage the workers came together and pooled their 

 results. It was seen that two different types of bacteria were 

 involved in the decomposition, or rotting, of straw. In the pre- 

 liminary stages, the " assimilating bacteria " were able to absorb 

 free nitrogen from the air, and by that means the straw was rotted 

 to a certain but very limited extent. The further rotting was 

 mainly due to the cellulose-decomposing organisms, and in order 

 that these might live and do their good work it was necessary 

 to supply them with food in the form of a nitrogen compound. 

 The problem of producing manure from straw thus became 

 simplified into one of supplying the cellulose organisms with a 

 cheap and effective source of food. Various ammonium salts 

 were tried, and it was found that entirely satisfactory results 

 could be obtained from the use of sulphate of ammonia, with 

 the addition of a certain quantity of chalk, varying according 

 to the composition of the water employed to wet the straw. 

 A method was thereupon devised for treating fairly large quanti- 

 ties of straw for the formation of manure. This method may be 

 briefly indicated. The required quantity of chalk is incorporated 

 with the straw in building up the stack ; the straw is then sprinkled 



