io8 



Journal of Agricultural Research 



Vol. XVIII, No. 2 



on basis of 50 cc. per plant. If in addition it were desired to maintain 

 the solution at approximately the same concentration and composition 

 at all times, many times this number of changes of solution would be 

 necessary. In this general connection it may be noted that Trelease and 

 Free (47) have given brief mention to an experiment in which it was 

 found that higher yields were obtained in cultures with a continuous 

 flow of solution. 



Table XIV — Approximate volumes of solution equivalent to total quantity of NO^ ab- 

 sorbed per plant 



[Nutrient solution containing 300 parts per million NO3] 



On basis of 50 cc. per plant, solutions would have to be changed from once daily to three or four times daily 

 to provide the quantity of N calculated from above absorption studies. If K or PO4 were present in low 

 concentration, large volumes of solution would also be necessary to supply these elements in the quanti- 

 ties capable of absorption. To maintain approximate constancy in solutions, verj' much larger volumes 

 than the foregoing might be required. 



It is of course unjustifiable to apply at all rigidly absorption data 

 obtained in one set of plant studies to another set, for the reason that 

 temperature or light conditions may in some cases be so unfavorable 

 that any large growth is impossible, and as a result absorption also will 

 be greatly diminished because the plant is stunted. Moreover, in the 

 first few weeks of growth absorption is comparatively slight; only when 

 plants are grown six weeks or longer will the full extent of absorption 

 become apparent. Some experiments dealing with concentrations and 

 ionic ratios have not been carried on for a sufficiently long time to give 

 an adequate idea of the effects of the various solutions tested. 



The statement is often made in texts on plant physiology that entirely 

 normal plants may be grov/n in solution cultures, but no data are given 

 concerning the yield per plant of grain and total dry matter. In fact, 

 only recently have detailed results been presented of systematic experi- 

 ments in which plants have been grown to maturity. In most of the 

 experiments the data and descriptions would indicate that the plants 

 obtained were decidedly inhibited by some factor, the total dry weight 

 per plant, height, number of tillers, etc. being usually less than for 

 similar plants grown under favorable conditions in the field for an equal 

 period. Various causes might be assigned to account for the diminished 

 yields. Obviously light or temprature may be unfavorable, and enor- 



