484 



SCIENCE 



[Vol. LV, No. 1427 



clear that reBewal ought to be move frequent 

 than with larger vessels, smaller plants, and 

 so forth. The labor involved is generally a 

 serious consideration also. Whether solutions 

 were renewed frequently enough, in particular 

 experiments, to allow growth to be correlated 

 with the characteristics of the solutions as 

 these were originally prepared has been a sub- 

 ject of discussion from time to time. To an- 

 swer this question for any experiment, a num- 

 ber of different renewal frequencies may be 

 simultaneously tested, to determine how often 

 the solutions must be changed in order that no 

 difference in growth may result with still more 

 frequent renewal. 



A consideration of this question, together 

 with the amount of labor involved in renewing 

 a large series of solutions, leads oljviously to 

 the suggestion that the solution might be made 

 to flow continuously through the culture vessel, 

 the inflow being of known composition and the 

 outflow being discarded. If the rate of flow is 

 rapid enough, the discarded solution will not be 

 significantly different from the inflow, and the 

 roots may be said to have been in a known set 

 of chemical surroundings throughout the cul- 

 ture period. Several rates of flow should be 

 simultaneously tested, at least in a preliminary 

 way, in order to make sure that the data 

 studied shall have been secured with a suffl- 

 ciently rapid rate. By employing continuous 

 flow, the labor of renewing solutions would be 

 practically avoided, since the apparatus would 

 operate continuously without alteration, aside 

 from the preparation of solutions and their 

 introduction into the appai'atus from time to 

 time. The apparatus should automatically 

 maintain any desired rate of flow through the 

 culture vessel. ^ 



The need of an apparatus for continuous 

 flow has become increasingly evident through- 

 out the recent development (begun by Schrei- 

 ner and Skinner, and Tottingham) of water- 

 culture experimentation by means of logically 

 complete series of salt combinations. A pre- 

 liminary step was taken when Trelease and 

 Free,^ working in this laboratory in 1916, con- 



1 Trelease, S. F., and E. E. Free : ' ' The effect 

 of the renewal of the culture solutions on the 



eluded that Shive's nutrient solution R5C2 

 (1.75 atm.) gave better growth the more fre- 

 quently the solution was renewed, a continuous 

 flow giving better growth than did daily re- 

 newal. Although, with the gradually improv- 

 ing technique of the water-culture method, 

 many workers- have doubtless appreciated the 

 desirability of continuous flow, constantly 

 flowing solutions appear not to have been sub- 

 jected to any further tests thus far recorded 

 in the literature.^ It is interesting to note, 

 however, that the logical need of continuously 

 renewed culture solutions was clearly stated by 

 Stiles.'' when he wrote: "In no case has a con- 

 stantly renewed culture solution been employed. 

 Thus the ratio of the variovis constituents was 

 probably constantly changing throughout the 

 experiments, and instead of being a constant 

 factor was an unknown and varying one." 

 Also, Duggar" mentioned the need of fre- 

 quently renewed or continuously flowing solu- 

 tions, but concluded that any operation involv- 

 ing continuous flow "would be impracticable 

 in most of our experimental work." 



This paper is planned to emphasize still fur- 

 ther the need of flowing solutions and to pre- 

 sent a brief description of an arrangement for 

 securing them. 



The accompanying diagram shows the main 

 features of the apparatus, which consists 



growth of young wheat plants in water-cultures. 

 Johns Rophins Univ. Circ, N. 8., No. 3, March, 

 1917, pp. 227 and 228. 



~ Conner, S. D., and O. H. Sears : ' ' Aluminum 

 salts and acids at varying hydrogen-ion concen- 

 trations, in relation to plant growth in water 

 cultures. Soil Science, 13: 23-33, 1922, p. 27. 



3 In 1865 Nobbe flowed solution into a vessel 

 in which plants were growing, but he seems not 

 to have tried to control the rate of flow. 



4 Stiles, Walter : "On the interpretation of the 

 results of water culture experiments. ' ' Annal. 

 Bot., 30: 427-436, 1916. 



' Duggar, B. M., ' ' Hydrogen ion concentration 

 and the composition of nutrient solutions in rela- 

 tion to the growth of seed plants. Annals Mis- 

 souri Bot. Gard., 7: 1-49, 1920, p. 43. — Idem., 

 ' ' The use of ' insoluble ' salts in balanced solu- 

 tions for seed plants." Ihid., 7: 307-327, 1920, 

 p. 308. 



