CH. in] WATER-CULTURE. 53 



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 Pythium, is the commonest cause 

 of failure in culture experiments ^ 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 

 cork should be taken out and put into the new cylinder, 

 but if for any reason the asbestos around the collars 

 should get damp it is better to take a fresh cork and to 

 fix the plant again with dry material. 



At the end of each week the plants should be changed 



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 Gheiranthus cheiri. 



