64 THE PLANT WORLD. 



tioned above and which lias other distinct advantages over the 

 ordinarv clav pot for certain forms of experiment, has recently 

 been devised by the Bureau of Soils of the U. S. Department of 

 Agriculture and bids fair to become widely used for determining 

 by the culture method the manurial and other requirements of 

 soils. This pot should prove of great value to anyone wishing to 

 perform physiological experiments on the effect of soil conditions 

 upon the growth of potted plants, for classroom or other purposes, 

 and for this reason the present paper has been prepared. 



The pot under discussion consists essentially of an artificial 

 hard-pan of the soil to be studied, in which the cement which holds 

 the grains together is ordinary hard paraffin. It is prepared as 

 follows : A pot or basket (Fig lo, a) three inches in diameter and 

 three inches high, made from galvanized iron wire netting of one- 

 eighth inch mesh, is inverted and repeatedly dipped to a depth of 

 about one inch in melted paraffin, until a firm paraffin ring or zone 

 is formed around the top margin (Fig. lo, b). The soil to be 

 used is then placed in the pot, having been first thoroughly mixed 

 and made up to the desired moisture content, and is pressed firmly 

 against the bottom and sides (Fig. lo, c). The pot is filled to 

 within about one-half inch of the top. The soil which has been 

 pressed through the walls and bottom is then brushed oflf and the 

 pot seized by the paraffined zone at the top and plunged in hot 

 melted paraffin, being held there until the paraffin has had time to 

 penetrate about one-eighth inch into the interstices of the soil. 

 The length of time needed for this operation varies, of course, 

 with the nature of the soil, a sandy soil requiring a shorter ex- 

 posure to the hot paraffin than a clay soil, since the interstices are 

 larger in the former. It is then removed and allowed to cool, 

 after which it is again dipped momentarily, this time in cooler 

 paraffin (Fig. lo, d). The purpose of the second dipping is to 

 form a firm layer of paraffin over the external surface of the walls 

 and bottom, to facilitate handling and lessen the danger of lireak- 

 ing the hard-pan formed by the previous treatment. When cool 

 the pot presents a uniform, smooth surface which covers the wire 

 netting on the outside, and it can be handled in the same manner 



