252 The Plant World. 



obtained'by weigbing the bottle and its contents at the begin- 

 ning and the end of the experiment. * 



The method here described was dev^eloped in order to 

 make a laboratory investigation of some potato soils. The 

 young potato plants, started as above described, without any 

 part of the tuber for support, were grown in extracts of soils 

 that gave good and poor yields in the field. The extracts 

 were made by shaking or stirring the soil with three times 

 its weight of distilled water and allowed to settle for thirty 

 minutes. At the expiration of that time the solutions were 

 filtered through the Pasteur-Chamberlin filter and put into 

 the culture bottles, details of which are described in the pub- 

 lications of the Bureau of soils, U. S. Department of Agricul- 

 ture, t The plants grew well in the extracts of the good 

 soil and a number of small potatoes formed. The tops were 

 thrifty and healthy. Figure i i shows these plants at the end 

 of the experiment. 



The seedlings in the poor soil extract made very little 



growth and did not produce any young potatoes. The ex- 

 tracts in both cases were renewed every fourth day, that is, 

 the old extracts were poured from the bottles and replaced 

 by a fresh supply. This prevents any detrimental effects due 

 to bacterial growth and always keeps a fresh supply of the 

 extract solvents to support the plants. It is not practicable 

 to grow the plants longer than five or six weeks in the water 

 cultures, which is sufficient time to indicate the relative pro- 

 ductivity of the soils and to show the effects of treatments. 



The method can be used as a means of research in a 

 number of lines of investigation. It is convenient for studying 

 the nutrient or stimulating value of various substances, in 

 connection with plant physiological investigations as well as 

 soil problems. An example to illustrate the nature of the 

 work done and the kind of results obtained is given in figure 

 12, 



' * Livingston, B. E., relation of transpiration to the growth of wheat. 

 Rot. Gaz. .40, 178-195. 

 .-t Bull. 23, Bii. Soils. 



