28 MICHIGAN ACADEMY OF SCIENCE. 



while those watered with non-sterilized soil infusions carried these tiiber- 

 clep. These experiments quite naturally suggested that the tubercles were 

 formed by the agency of bacteria, and microscopic and cultural studies 

 confirmed this supposition. Soon the characteristic microorganisms in 

 these tubercles were obtained in artificial culture media and their causal 

 relation to the tubercles was proved by direct inoculation experiments. 

 Moreover peas were planted in sterilized soils and watered with these cul- 

 tures. When this was done it was found that tubercles formed abun- 

 dantly on the roots of the plants, which, on account of their ability to fix 

 nitrogen, grew vigorously and produced abundant crops. Additional 

 studies have shown that these bacteria, which are quite widely distrib- 

 uted in the soil, pass into the roots, forming the swelling or tubercle at 

 the place of entiance, penetrate the woody tissue in the form of delicate 

 filaments, and produce a mucilaginous substance which permeates the 

 tissues of the plant.. There has been some discussion as to whether it is 

 the bacteria or the plant which fixes the nitrogen, but the only conclusion 

 which can b? justified by the experiments that have already been made is 

 that both of tliese organisms are essential, both the germ and the legumi- 

 nous plant aie necessary, and they must act together in order to take 

 free nitrogen from the air and combine it into the tissues of the plant. 

 1 should state that some experiments indicate that there is a certain 

 amount of nitrogen fixation in the green parts of many plants, but this 

 is so very small compared with the large quantities fixed by the combined 

 action of leguminous plants and the bacteria that it cannot be considered 

 to be of any special importance. In this way it will be seen that there is 

 an association between the plant and the microorganism which is mutu- 

 ally beneficial to the two, and which enables the tv/o working together to 

 take free nitrogen from the atmosphere and build it up into tissue 

 which can be subsequently utilized for feeding other plant? and even 

 nourishing animals as well. Some experiments indicate that there are 

 different species of the tubercle organism, and that it is necessary in order 

 to get the best results to bring together the special legume and the special 

 tubercle bacillus which best work together. 



It will be seen from this that bacteriology has been a benefit to the 

 world not only by decreasing sickness and lessening the death rate, but 

 also by pointing out to the farmer a way by which he can utilize the in- 

 exhaustible stores of free nitrcgen in the atmns])here as a fertilizer for 

 his soil. ]\Inrpover it has placed within the hands of man the means by 

 which under intelligent direction the abundance and vigor of life in this 

 world can be increased. It shows us how it may be possible for the arid 

 sandy plain to be converted into a rich field, and how waste ])laces may 

 be fertilized and made to yield abundant food for plant and animal. 

 Just ( ne bundled years ago Sir Humphrey Davy in a popular lecture 

 before the Royal Institution used the following words: "The j)rogression 

 of p' ysical science is much more connected with your prosperity than is 

 usually imngine.i. You owe to experimental philosophy some of the most 

 important and peculiar of your advantages. It is not by foreign con- 

 quests chiefly that you are to become great, but by a conquest of nature 

 in your own country. It is not so much by colonization that you have 

 attained your prominence or Avenlth, but by the cultivation of the riches 

 of your own so'l. Why at this moment are you able to sunply the world 

 with a thousand articles of iron and steel necessary for the purposes of 



