510 Scientific Proceedings, Royal Dublin Society. 



pressure due to a head of 30 cms. The water had been boiled and allowed to 

 cool until it was a little warmer than the temperature of the laboratory. The 

 boiling removed the dissolved gases, and so there was less danger of bubbles 

 blocking the canals or the supposed perforation in the membrane. The result 

 was that drops issued from the pore in the same way as they did when the 

 tip was attached to the leaf, and in twenty hours 6c.cs. of water were 

 collected. 



The experiment was repeated, substituting a 03 per cent, solution of starch 

 for the water. Liquid came through the pore as before, and when tested 

 with Liquor Iodi turned blue, showing that starch had gone through, and 

 proving that there could be no continuous membrane located between the 

 water channels and the depression. 



In all cases where leaves or tips had to be brought into the laboratory 

 from Trinity College Gardens, they were kept as damp as possible, by being 

 packed in wet Sphagnum moss, or put in a bottle in warm water that had 

 been boiled and allowed to cool. This lessened the risk of nagging, consequent 

 injury to the tissues, and the entrance of ab: into the canals. 



From the results of these experiments it did not seem possible that the 

 exuded water could be a secretion from a gland in the leaf-tip, as it is usually 

 supposed. In order to test this further, the tip of a young leaf, while still 

 attached to the plant and working vigorously, was anaesthetized. To do this, 

 a small bottle was carefully washed free from grease, and the interior coated 

 with glycerine and water, in order to prevent globules of dew forming on the 

 glass and obscuring the view of what was going on inside. Some chloroform 

 was poured in, and the tip of the leaf introduced into the bottle. The back of 

 the leaf rested against a cushion of plasticene, so that the veins would not be 

 injured by pressure against the glass. The neck of the bottle, after the 

 introduction of the leaf, was closed by a plug of cotton wool. The tip was 

 suspended in the chloroform vapour, in such a manner that the liquid anaes- 

 thetic did not touch it. Before introduction into the anaesthetizing vapour, 

 the leaf was producing sixteen small drops per minute. The experiment was 

 started at 8.25 a.m., and the tip of the leaf was left in the bottle till 9 a.m. 

 Exudation continued at the same rate throughout, but by 9 a.m. both the 

 tip and the water exuding from it were discoloured. At 9 a.m. the tip was 

 removed from the anaesthetizing chamber and washed, and at 9.30 a.m. it 

 was still acting at the same rate. This result supported the view that the 

 water was not secreted by glandular action at the tip of the leaf, because if 

 glandular action there had been its source, the exudation would have become 

 slower or would have ceased entirely during the application of the anaesthetic. 



