60 WATER- CULTURE. [CH. Til 



The culture solution should be boiled rapidly for at 

 least half-an-hour, the water which evaporates off being 

 replaced from time to time with pure distilled water, and 

 transferred to the cylinder as soon as it has cooled. 



Two holes should be cut in the cork, one for the plant 

 and one for a tube to admit air to the interior of the 

 cylinder. For the latter purpose a short glass tube is 

 inserted through the hole in the cork so that the ends 

 project about 5 cm. beyond the upper and under surface; 

 the upper open end is attached to a small bulb tube 

 loosely packed with recently ignited asbestos which will 

 exclude dust etc. but allow a circulation of gases. This 

 tube is also useful for introducing fresh water, when 

 required, without touching the plant, as it is only 

 necessary to remove the bulb tube and afterwards replace 

 it. 



To fix the plant in position in the cork, soft asbestos 

 which has been recently heated is preferable to cotton- 

 wool, and the material should not project beyond the 

 lower surface of the cork, as it is desirable to keep it 

 as dry as possible, since 'damping off' at the 'collar,' 

 from the attacks of fungi, is the commonest cause of 

 failure in culture experiments 1 . For the same reason, 

 only those plants should be selected for use which are 

 uninjured at the ' collar,' and great care taken that no 

 injury is inflicted at this part when fixing in position. 

 When changing the plants into fresh cylinders the whole 



1 Out of fifty-six unsuccessful experiments where plants died within 

 three weeks, more than thirty were attacked in this way ; the plants were 

 seedlings of Epilobium hirsutum and Cheir&uthtu cheiri. 



