crock is slightly jarred to settle the sand about the roots of the 

 plants and to give a flat surface for the wax seal. 



An aspirator is now connected to the suction tube and the 

 excess of solution is drawn off until the moisture content of the 

 sand is reduced to about sixteen per cent, (dry-weight basis). 

 The sand is then flooded a second time with nutrient solution, and 

 the excess is again removed, as just described. The aspirator 

 tube should be joined to the culture tube with a suitable bottle 

 intervening as a trap to catch the solution that is removed. This 

 bottle is to be marked so as to indicate when the desired volume 

 of solution has been removed, a device that will save many 

 weighings if the volume of solution added is known. The weight 

 of the seedlings may be neglected and the required moisture 

 content of the sand may have any value between fifteen and sev- 

 enteen per cent, (dry- weight basis). 



The Wax Seal. To hinder evaporation from the soil, the free 

 sand surface is sealed with a mixture of eighty parts (by weight) 

 of "Parawax" and twenty parts of "Vaseline, White" (Ches- 

 brough brand). Have the mixture only warm enough to flow 

 freely, otherwise the plants may be injured where their stems 

 are in contact with the seal. Pour the wax over the sand sur- 

 face, so as to form a layer from two to four millimeters thick, 

 being sure that the wax forms a tight joint at its junction with 

 the crock wall and with the supply cone, also that it makes good 

 contact with the seedling shoots. (On wax seals, see : Briggs and 

 Shantz, Bot. Gaz. 51: 210-219. 1911.) 



Manipulations During the Culture Period. At the end of each 

 314-day period each culture is weighed, and suflficient distilled 

 water is added (through the cone) to bring the sand moisture 

 content back to the original sixteen per cent,, and record is 

 kept of the amount of water needed. Then the excess liquid is 

 removed (aspirator) until the moisture content is about ten per 

 cent. Then the sand is again flooded with fresh solution and the 

 excess is once more removed, this time leaving the moisture con- 

 tent at sixteen per cent. The culture is then ready for the suc- 

 ceeding 31/^-day period. 



From the records showing the amounts of distilled water 

 added to any culture are to be obtained data of transpirational 

 water loss. It will be seen that the amount of salt absorbed by 

 the plants is neglected (as though the plants absorbed only water 

 from the solution), but the error thus introduced will be more 

 truly negligible than the one that would be encountered if 

 nutrient solution were used in place of distilled water. 



49 



