the reproductive phase, when the plants have previously been 

 supplied with the respectively best solutions for the germination, 

 seedling and vegetative phases. 



Plant Measurements at End of Reproductive Period. These 

 are to be generally the same as those made at the ends of the 

 preceding periods, but it will be desirable to separate the grain 

 produced from the rest of the tops in the present case. The dry 

 weight of grain is to be determined, also the number of grains. 

 Of course visual observations are to be made from time to time 

 during the reproductive phase, with special attention given to 

 flowering and fruiting. 



Renewal of Solutions. 



The solution placed in any culture jar as the beginning of an 

 experiment is to be completely discarded and replaced by a fresh 

 one of the same composition, after 31/2 days, and this renewal of 

 every solution is to occur at 31/2 -day intervals (twice per week, 

 thus avoiding Sunday renewals) throughout the course of the 

 experiment. The following points apply to all growth phases 

 alike. 



Before the renewals are to be made, a new set of jars are pre- 

 pared, as at the beginning, each filled with its proper solution 

 and properly marked and stoppered with non-perforated cork. 

 Then these jars are placed near the series of cultures and each 

 stopper, bearing its plants, is removed from its original jar and 

 placed in the new jar of corresponding number. In making the 

 change, care is of course to be taken not to injure the roots nor 

 to disturb them more than is unavoidable. Finally, the opaque 

 jackets are transferred to the new jars, and the old jars are 

 emptied, the volume of the contents is recorded, and they are 

 washed, to be used again at the next renewal. 



The purpose of determining the volume of solution remaining 

 in each jar at each renewal is to furnish data on the relative 

 amounts of water absorbed by the various cultures. The volume 

 of solution originally placed in each jar will of course be known, 

 and this value minus the volume left after 31/2 days will repre- 

 sent the volume absorbed in that period. The rate of absorption 

 is approximately the same as the rate of transpiration for such 

 plants as we deal with. Of course this volume measurement 

 need not be of great precision ; a plus or minus error of as much 

 as 3 or 4 per cent, is probably allowable until results indicate 

 necessity for greater precision. It should be added that a better 

 method of dealing with this feature is to weigh each culture be- 



» 19 



