May 5, 1922] 



SCIENCE 



485 



essentially of four parts : the upper reservoir 

 (E), the constant-level tank (L), the lower 

 reservoir (0), and the culture vessel (V). The 

 upper reservoir' (R) holds 5 gallons of solu- 

 tion when full, and acts like a constant-pressure 

 aspirator, drawing air through tube A'A and 

 delivering solution through the siphon tube 

 (B), to the constant-level tank (L). The latter 

 is a piece of 5-cm. glass tubing closed below by 

 means of a rubber stopper with three tubes, 

 B, E, and D. Solution flows into the tank 

 through tube B, at a rate somewhat gi-eater 

 than is required for the culture vessel, and 

 the excess passes into the lower reservoir (O), 

 through the tube E, the tank level being auto- 

 matically maintained at the top of the last- 

 mentioned tube. The rate of flow through B is 

 adjusted by adjusting the height of the lower 

 end of tube A with reference to the upper end 

 of E. Solution flows at a practically constant 

 rate from the constant-level tank, through a 

 small-bore delivery tube (D), and drips I'egu- 

 larly into the thistle-tube receiver (F) of the 

 culture vessel. The desired rate of flow 

 through tube D is secured by adjusting the 

 height of the upper end of E with reference to 



the lower end of D — that is, by adjusting the 

 "head" maintained by the constant-level device. 



The culture vessel shown is a 3-gallon, glazed 

 earthenware "butter" jar, covered by a paraf- 

 fined top, of wood, cement or plaster of Paris, 

 with eight large openings, in which are set 

 the flat cork stoppers that support the plants. 

 There are five wheat seedlings in each stopper, 

 forty seedlings in all. The top is supported 

 about 4 mm. above the top of the jar. The re- 

 ceiver tube (F) has a waxed-paper cover, 

 through which passes the delivery tube. Tube 

 F extends nearly to the bottom of the culture 

 vessel, and solution flows into the latter, keep- 

 ing it filled to the brim and overflowing at the 

 top, through the waste tube (G). 



Solution that collects in the lower reseiwoir 

 (0) has not been vitiated in any way by its 

 passage through the constant-level tank, and 

 it is raised to the upper reservoir (R) from 

 time to time, together with additions of newly 

 prepared solution. This transfer is effected 

 through the tube A" A, by closing cocks A' 

 and B' and applying suction at C (by means 

 of an ordinary filter pump). When the trans- 

 fer is completed, cock C is closed and cocks 

 A' and B' are opened. 



The reservoirs should be covered with opaque 

 paper, to exclude nearly all light and retard 

 the development of algas. 



The constant level device and the lower reser- 

 voir may be dispensed with entirely if the tem- 

 perature of the upper reservoir can be main- 

 tained practically constant, or if only an ap-' 

 proximately constant rate of delivery of solu- 

 tion is desired. In this case, tube B would 

 discharge directly into the receiver tube (F). 

 This simpler apparatus is the one employed 

 by Trelease and Free. 



Doubtless, the apparatus here described may 

 be modified in many ways, to suit the facilities 

 and requirements of different experimenters; 

 but this foi'm operates very satisfactorily. As 

 thus far used, a series of five are delivering 

 five different solutions to their respective cul- 

 ture vessels at a rate of about 16 liters a day, 

 which amounts to 400 c.e. a day for each of 

 the forty plants in the culture. With liter 

 jars, five plants per cultui'e, and solution re- 

 newal every three and one half days (as in 

 the plan published by the National Research 



