508 



Scientific Proceedings, Royal Dublin Society. 



a definite perforation in one of these lamellae, was noticed, connecting two of 

 the intercellular spaces (Text fig.)- No epithem was observed. All these 

 features, the lacunae in the petiole, the canals in the leaf, the spaces and 

 perforations in the mesophyil, point to arrangements for a rapid transfer of 

 water up the petiole and through the blade. This does not support the 

 hypothesis that the water is secreted by cells in the tissues of the apex, or 

 even filtered there. 



In order to find if continuous membranes responsible for filtration 

 existed under the pores in the depression, tips of leaves were embedded in 



Vertical section of leaf, showing perforation (P)in lamella dividing the spaces 

 in the mesophyil. (From a photograph.) (x 200.) 



paraffin wax and sectioned. Although numerous attempts were made, and 

 traces of what might have been a membrane, separating the cavity of the 

 pore from the canals running into the leaf-tip, were found, the membrane was 

 always discontinuous, and no case of complete continuity was demonstrated. 

 The great objection to this method was that a discontinuity might be pro- 

 duced by unequal contraction and subsequent shrinkage during embedding, 

 or by tearing during sectioning. 



It thus seemed impossible to decide by histological investigation, and it 

 was evident that some physical method would have to be adopted, and 

 attempts were made to induce a colloid to pass through the pore into the 



