THE POOD OF PLANTS. 67 



to the Papilionaceae, is the organism which at the cost of elemen- 

 tary Nitrogen, clearly with the assistance of the carbohydrate 

 supplied by the Papilionaceae, produces proteid. When the 

 tubercles empty, and the bacteroids disappear from their cells, 

 the proteid passes into the organs of the plants, and is here 

 employed in nutrition. If the soil in which, e.g., peas are develop- 

 ing contains no Nitrogen compounds, then from what we have 

 seen the development of the plants is only possible when the 

 roots, by infection with Bacterium Radicicola, come to form 

 tubercles, and for this reason only those of our objects exhibited 

 considerable power of development which grew in unsterilised 

 soil, or in sterilised soil watered with fresh soil-extract. 



For the method of preparing pure cultures of Bacterium 

 Radicicola, see Prazmowski, Versuchsstationen, Bd. 37, pp. 197 and 

 199, and also Beyerinck, Botan. Zeitung, 1888. Prazmowski (see 

 p. 198) has also made investigations which teach that bacteria 

 taken from pure cultures induce formation of tubercles on the 

 roots of peas when the soil in which the objects are growing is 

 infected with the fungus, while without such infection tubercle 

 formation does not take place. Finally we find in Prazmowski 

 (Versuchsstationen, Bd. 38, p. 20) directions for experiments, which 

 by a very exact but also very complicated method enable us to 

 prove that only Bacterium Radicicola, and no other form of 

 Schizomycete, can bring about the nutrition of Papilionacese by 

 means of elementary Nitrogen.* 



In the course of Practical Plant Physiology which I conduct I 

 include experiments intended for general information on the 

 nutrition of plants with free Nitrogen, and proceed as follows : 

 Suitable glass cylinders capable of holding about 2'5 kilo- 

 grammes of sand are filled to a depth of 1-2 cm. with ignited 

 quartz. To every 2'5 kg. of the sand referred to above are added 

 in a large dish 375 c.c. of distilled water, 0375 gr. H 2 KP0 4 , 

 0-200 gr. KC1, 0-200 gr. Mg S0 4 , 10 gr. Ca C0 3 , together with 

 some phosphate of iron, and the mixture is crumbled into the 

 cylinders. Each cylinder receives in addition 10 c.c. of soil- 

 extract, prepared by treating 10 gr. of soil from a pea field with 

 100 c.c. of water. The quantity of Nitrogen compounds in such 

 an extract is so slight that it may be neglected. Some cylinders 



* It may further be remarked that we provisionally designate by the name 

 Bact. Eaclic. not merely one, but a whole group of Schizomycetes, which are of 

 importance in the nutrition of the Papilionaceas. 



