66 THE PLANT WORLD. 



ing, by weighing", the amount of transpiration from plants in these 

 pots it is only necessary to seal the upper surface with a piece of 

 paraffined paper cemented by means of paraffin to the pot walls 

 having this fit closely against the stems of the plants. In the case 

 of loamy or clayey soils if water is to be added to the soil from 

 time to time to keep its moisture content uniform, it is well to 

 cover the soil surface with a thin layer of clean sand, which pre- 

 vents puddling and facilitates the equal distribution of the water 

 added. 



Seedlings grown in these paraffined wire pots exhibit a perfectly 

 normal distribution of roots throughout the soil mass. The par- 

 affin is harmless and exerts no injurious influence upon the plants. 

 Fig. 1 1 shows the soil masses of two cultures of six wheat plants 

 each, a having been grown in a pot of the paraffined form, and b 

 in a glass beaker of the same size. The points brought out in the 

 discussion are very evident, the soil mass from the paraffin pot 

 showing practically no roots on its surface, while that from the 

 beaker has its lower surface nearly covered. The first soil mass 

 was found to be completely filled with well-branched roots, the 

 second contained very few except near its lower surface. With 

 plants having small roots it is very rarely that these organs pene- 

 trate the wall of the paraffined pot. Plants with larger roots 

 often penetrate, however, and thus such plants are not well 

 adapted to this method. Wheat and the smaller grasses serve 

 admirably, while Indian corn often forces its roots through the 

 bottom of the pot. 



The culture method above described appears to offer the best 

 means yet devised for determining or demonstrating the influence 

 of soil conditions upon the growth of seedlings. It* may be used 

 for studying the effect of different moisture contents of the soil, 

 for determining the relative productiveness of different soil 

 samples, for studying the effects produced by the presence of 

 various substances in the soil, and for many other lines of experi- 

 mentation. 



