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the left-hand solenoid and the tube passing through it is drawn back, with the result that the water drops can 

 now fall into the soil of the pot through the glass tube provided for the purpose. As the drops continue to fall 

 the left hand pan slowly sinks and the other pan rises and so completes the circuit through the pair of 

 platinum points on the right side. A current then flows through the right-hand solenoid, with the result that 

 the tube is brought back into its forward position and its funnel again receives the falling water drops. 

 The tube remains in this position until the plant has transpired aa amount of water equal to that added, 

 when the circuit is again closed by the rising of the pan. 



Every time the right-hand pan completes the circuit a portion of the current passes through the pen and so 

 gives a record on the drum of each addition of water to the pot. By altering the adjustment of the pair of 

 platinum points the apparatus can be set to respond to any number of drops, so that even small and slowly 

 tianspiring plants can be made to give records at short intervals. The actual weight of water lost which 

 corresponds to each mark on the record is obtained by catching the appropriate number of drops in a weighed 

 vessel and noting their weight. The drops should be allowed to fall slowly, as owing to the damping arrangement, 

 the response of the pans to slight differences of weight is somewhat sluggish. 



The amount of water in the soil is kept constant throughout the experiment, and thus a falling off of trans- 

 piration due to a decreasing moisture of the soil is completely obviated. The solenoids are provided with " cut- 

 outs," so that the current only passes momentarily at the time the points first make contact with mercury cups 

 on the pans ; there is thus no sparking from these points, and the position of contact is kept constant. A few 

 drops of oil should be placed on the surface of the mercury of the " cut-outs " ; the volatilization of mercury on 

 sparking is thus prevented. The apparatus requires an E.M.F. of about 3 volts, and so can be worked with 

 two Leclanch6 cells or by storage batteries. 



(For further details see " Annals of Botany," Vol. XXVII., 1913.) 



4517 4522 4523 



4517 T Demonstration Clinostat, with clockwork drum to revolve once in fifteen minutes 



4 11 9 



We are always prepared to make any special apparatus to order, and also to make and supply 

 any of the apparatus figured in text books on plant physiology. The following apparatus are taken 

 from Detmer's Moore's " Practical Plant Physiology " : 



4518 Glass Jar for apparatus. Fig. i, page 4 . . . . . . . . ..016 



4519 Glass Vessel with parallel walls. Fig. 7, page 25 .. . . . . . . ..050 



4520 Sach's Bell Jar, lof by 4! in. Fig. 9, page 28 . . . . . . . . ..0170 



4521 Glass Bottle. Fig. 10, page 28 .. . . . . . . . . . . ..030 



4522 Apparatus for the culture of plants in a space devoid of oxygen. Fig. n, page 34 . . 040 



4523 Apparatus to prove that green plants can only produce oxygen when CO 2 is at their 



disposal. Fig. 15, page 40 . . . . . . . . . . . . ..046 



CROSS STREET HATTON GARDE1ST, E-C 



