208 



Scientific Proceedings, Royal Dublin Society. 



pressure, may be explained as an effect one would expect due to the dilution 



of the poisons. 



As further supporting the explanation which I have previously given of 



the observed wilting, the two following experiments carried out in the summer 



of 1911 may be of interest. 



The object of these experiments was to see if it would be possible to more 



or less completely wash out tlie poisonous material from the killed region, 



and so prolong the life of the leaves above that region. 



The subject of the first experiment was a pot-plant of Primus Cerasiis 



(fig. 1). The stem of this plant bifurcated at a level of about 40 cm. above 

 the soil into two equal branches B and C. B pro- 

 duced two lateral branches E and D at 11 cms. and 

 34 cms. respectively above tlie bifurcation, while C 

 had two smaller leafy branches about 15 cms. above 

 the bifurcation, and terminated with a tuft of leafy 

 branches above. The top of B above tlie base of D 

 was removed, and, with suitable precautions to mini- 

 mize tlie clogging of the surface, a rubber-tube was 

 attached to it. The whole of E, except a few centi- 

 metres of its base, was cut away. The cut surface at 

 the top of B was now supplied with distilled water 

 under a head of 33 cms., and when the cut surface 

 of E, by becoming moist, showed the arrival of the 

 stream below, the intervening space of 23 cms. (shown 

 dark in the figure) was lapped in cloth and sprayed 

 with boiling-water. Meanwhile the leaves were 

 protected from injury by being covered with damp 

 cloths. The hot spraying lasted ten minutes. After 



Expt. 1. The dark region on it ceased the damp cloths were removed from all 



the brancli.Bindicates the part gxcept the branch D. The transpiration of this 



■B'hich was tilled at the begm- , , , , , . . ^ ■ , , 



iiino- of the experiment. Tlie branch was thus kept at a minimum during twenty- 

 shaded region on branch C fo^r hours, wliile the supply of distilled water was 

 shows the part heated later. , n ^ , n , ■ i j i • i j_i 



kept up to nush out the materials exuded into the 



water-ways of the heated region. During this time about 35 c.cs. were passed 

 in at the top of B. After this the plant stood in a cool green-house under 

 conditions favourable to transpiration. 



Three days later it was observed that the lower leaves of D and a few of 

 the leaves at the lower branches of were slightly discoloured and curled at 

 the edges — typical symptoms of the poisoning caused by heating the supply 

 branch. Evidently heating part of B had affected not only the leaves above 

 it, but also the effects had been transmitted backwards to C. 



Fig. 1. 

 Plant of Friimis Cerasus used in 



