APPLICATION OF SCIENCE TO PLANT CULTURE. 93 



Mr. Bowker asked if an increase of carbonic acid gas in the 

 soil would have the desired effect. 



Professor Atwater replied that it was only lately' that we had 

 got acquainted with the microbes, and we know but little about 

 them. The}' are present within the air and without ; we cannot 

 live without them and we cannot die without them. It was only a 

 dozen years ago that the first discover}' was made of their relation 

 to the supph' of nitrogen to plants. The theory is that microbes 

 are efficient in enabling the plant or the soil or both to avail 

 themselves of the nitrogen. The speaker reminded his hearers 

 of Hellriegel's suppositions on this point, and his experiments 

 shoveing that when infusions containing bacteria are used the 

 plants do get nitrogen, and that when they do not have the 

 infusions, the\' do not get a supply of nitrogen. He also alluded 

 to the " humus theory " formerly held — that humus is the food of 

 plants — until Liebig went out on a sandy knoll and demonstrated 

 that humus is not a necessity. Still it is efficient in furnishing food. 

 Carbon in plants is taken up from the air by their leaves ; in the 

 soil it is efficient in promoting the decomposition of the rocks and 

 furnishing plant food. The same material makes food and lodging 

 for bacteria. The presence of organic matter in the soil would 

 increase bacteria. The whole subject is a new one ; but two 

 journals devoted to bacteriolg}' have been started within a short 

 time. To the question how to favor the action of bacteria he 

 would reply that we must favor the cultivation of such plants as 

 gather them. They supply the nitrogen of cattle food. It used 

 to be thought that corn stalks were of no value because they lack 

 protein and nitrogen. If it shall prove that corn has this happy 

 facult}' of gaining nitrogen from the air, so much the better. 



Mr. Philbrick asked if it was not possible that the prevailing 

 prejudice among farmers in favor of animal manure might be 

 justified by its promoting the growth of bacteria and consequently 

 the liberation of nitrogen. 



Professor Atwater replied that this seemed a very plausible 

 hypothesis. As a scientific man he has a great respect for the 

 practical results of the labors of practical men. We find b}' 

 experiment that the commercial fertilizers do surpass the barnyard 

 manure in supplying plant food, yet despite this he felt that there 

 must be something to justify the prejudices of farmers in favor of 

 the latter. The organic matter in the soil, favored by the higher 



