226 Scientific Proceedings^ Royal Dublin Societi/. 



Salix lahylonica, and Coioneaster frigida. In the last-mentioned, however, 

 much larger quantities of reducing sugars were found present in the sap of 

 the steamed branch than could have been formed by the inversion of tlie 

 non-reducing sugars present in the sap of the fresh branch, so that we must 

 assume that they were iutroduced into the sap from the neiglibouring cells. 



These tests are sufficient to justify the surmise that the physical and 

 chemical nature of the sap is profoundly altered by steaming the branch 

 througli which it passes. 



It is evident that the substances thus introduced into the sap must be 

 swept along in the rising current till they reach the leaves, except for the 

 material which is absorbed by the walls of the tracheae, and by the cells 

 adjoining the water tracts above the heated region. In the leaves those 

 which are not in a form suitable for assimilation must accumulate ; and 

 if sufBcient of the branch has been killed, the accumulation will ultimately — 

 without any other poisonous action — plasmolyse the cells of the leaf.' 



Eeduction in the water-supply may be also brought about by the coagula- 

 tion of colloids in the sap, and tlie consequent formation of plugs in the 

 conducting tubes. This condition has been observed by several investigators.' 



It seemed of interest to essay to find out if the sap in steamed branches 

 contained any substance which acted as a protoplasmic poison, and not 

 merely as a plasmolysing agent by simple accumulation. To test this point 

 saps extracted from branches subjected to various treatments were applied to 

 severed leaves of Elodea canadensis, and the effect ou the cells of these leaves 

 was microscopically controlled. 



In the first place it was found that the cells remained normal, and proto- 

 plasmic streaming continued undiminished in tlie sap from fresh branches 

 for at least five days, and probably much longer. This point was verified in 

 the case of the sap of Ilex AquifoUum, Primus cerasus, Syriiiga vulgaris 

 Cotoneaster frigida, and Salix hahylonica. In contrast to the sap from the 

 fresh brandies, tliat from the steamed branches of all of these, with tlie 

 exception of Ilex AquifoUum, produced lethal changes in the leaves of Elodea 

 within two or three days. These changes consisted in a cessation of 

 protoplasmic streaming, in the discoloration of the veins and margins, and 

 in the contraction of the protoplasts of the cells all over the leaf, and their 

 ultimate blackening. The contraction which occurs is not of the nature of 

 plasmolysis ; for more than a day is often required for its production, and 

 it cannot be undone by the transference of the leaf into water. 



' It may be noted that Ursprung looked for plasmolysing ett'ects in the root-hairs of Impntiens 

 Sttllani hy a decoction of the same plant, but did not find any. Here, of course, cpncentration 

 would not take place. ^ J. B. Overton, loc. cit. 



