November, 1908,] 



469 



Scientific Agriculture. 



power than is possessed by these free 

 living organisms may probably be 

 assigned to the 



Nodule Bacteria, 



During a certain period of their 

 existence these bacteria are living free 

 in the soil, but it is not known whether 

 they multiply under such circumstances. 

 When, however, they insinuate them- 

 selves into the hair-rootlets of plants, 

 especially those of the leguminosae, they 

 produce upon them swellings or nodules, 

 wherein they multiply enormously. 

 They then actively assimilate atmos- 

 pheric nitrogen, and in some way benefit 

 the host plant. How this is brought 

 about is not yet understood, in the face 

 of the fact that the higher plants require 

 nitrogen in the shape of nitric acid to 

 feed them. The fact that these quasi 

 parasites materially benefit their host 

 by the assimilation of aerial nitrogen, 

 however, has been established without 

 reasonable doubt by repeated experi- 

 ments. Pots filled with sterlised soils, 

 one of which was inoculated with nodule 

 material, have proved the effect. The 

 inoculated pots yield larger crops, and 

 nodules had been produced on the roots 

 of the plants, whilst on the plants 

 of the uninoculated pots no nodules 

 occurred. In the field many similar 

 results were obtained, and inoculation 

 with artificially reared nodule bacteria 

 has produced remarkable results. On 

 the other hand very many inoculations 

 in the field did not in the least benefit 

 the crops. This non-success of inocula- 

 tion in the greater number of instances 

 in my opinion is mainly due to the 

 previous presence of the bacteria in the 

 soil experimented upon. The want was 

 already supplied and inoculation was 

 not required. 



A difference of opinion still exists as 

 to whether the nodule organisms found 

 on different plants are distinct, or 

 merely varieties of the same species. 

 Latest researches tend towards the 

 latter opinion, and probably, correctly, 

 as recently some German experimen- 

 talists have made the nodule bacteria 

 of French beans, after two or three 

 generations, effectively accommodate 

 themselves to other leguminosse. But 

 this is merely an absolutely scientific 



question ; the fact remains that these 

 bacteria are so different in their 

 character as to require for successful 

 inoculation that the soil on which the 

 particular crop is grown must be in- 

 oculated with cultures taken from the 

 nodules of similar plants. 



These nodule bacteria, like the other 

 nitrogen assimilating organisms and the 

 nitrifying bacteria, are also emphati- 

 cally aerobic ; neither they nor the other 

 kinds can, consequently, live deep in the 

 ground. At a depth of from 4 or 5 

 inches from the surface they generally 

 thrive well ; below 6 inches they begin 

 to occur sparingly, and deeper than 

 9 to 12 inches they are only found under 

 exceptionally favourable circumstances. 



The benefit lucerne fields receive from 

 harrowing in spring is no doubt partly 

 caused by enhancing the bacterial acti- 

 vity through the aeration of the soil 

 surface. 



In conclusion, I draw attention to the 

 universal axiom, that nature constantly 

 works with exceedingly small quantities. 

 As an example we may take one of the 

 nodules attached, say, to roots of 

 lucerne ; not a millimetre in diameter, it 

 frequently contains from 500,000 to 

 1,000,000 of bacilli, and yet every indi- 

 vidual of these assimilated some nitro- 

 gen. When we consider the minuteness 

 of the individual organism, how infi- 

 nitely small must be the quantity of 

 nitrogen absorbed by it. Even the 

 quantity fixed daily by a milliou is so 

 minute that the most delicate balance 

 would scarcely weigh it, and chemists 

 can weigh to the one hundred thousandth 

 part of a gramme. According to 

 Paul Herre, 2,000,000 of organisms only 

 weigh one milligramme (the thousandth 

 part of a gramme). The number con- 

 tained in an acre of soil in order to 

 bring about the assimilation of 10 to 20 

 lb. of nitrogen is, therefore, so prodi- 

 gious, that expressed in figures they 

 would cover a couple of lines of this 

 page. Bacilli vary in size, but it takes 

 generally from 15,000 to 30,000 laid 

 lengthways to measure an inch, and yet 

 the results produced by them in a very 

 short time are considerable. — Agricul- 

 tural Gazette of New South Wales, 

 August, 1908, Vol', XIX, Part 8. 



