228 Scientific Pt'oceedings, Royal Dublin Society. 



It may be noted that, in the case of Cotoneasterjrigida, Syvinga vulgaris, and 

 Ilex AquifoHum (see foot-note on previous page), the liquid centrifuged from 

 the steamed brancli, after it was emptied of sap and filled with water, is 

 more rapidly poisonous than the sap itself. In these cases probably a poison 

 is formed in the cells after death, which is not sufficiently concentrated in 

 the sap centrifuged immediately after steaming. The same explanation 

 probably applies to the observation that the sap extracted from the Syringa 

 branch immediately after steaming is not so quickly lethal as that drawn 

 off a couple of days after death. 



The slow generation of poisons indicated in these experiments probably- 

 affords an explanation of the fact that, even when steamed branches are 

 washed out immediately after the heating, some of the leaves above perish 

 from poisoning.' 



The facts recorded in this note form additional evidence against the 

 view that the leaves above a steamed branch perish because they are cut 

 off from their water-supply by the death of the cells of the stem. They 

 show that in every case profound changes are produced in the sap by the 

 steaming, which will ultimately cause plasmolysis of the leaf-cells if these 

 cells are not previously killed by poisonous substances produced in the heated 

 region. The immediate or ultimate production of these poisons has been 

 demonstrated in all the cases examined. As has been pointed out previously, 

 the drying of the poisoned leaves is probably caused by the partial or complete 

 plugging of the water-channels by colloids exuded from the heated cells, or 

 coagulated in the sap. 



1 Henry H. Dixon : " Spread of Morbid Changes through Plants from Branches killed by Heat."" 

 Proc. Eoy. Dublin Soc., toI. xiv, No. 12, 1914, p. 205. 



