?RESIDENTtAL AtiDRESS* 901 



tionS of stimulation upon our horizon. We may therefore postpone speculation 

 upon the mechanical principles governing them and await the time when by 

 scientific oiierations we shall have reduced to law and order the intervening 

 region, which wo may entitle the chemical substratum of life. This done we 

 may venture to pitch our laboratory a march nearer to the phenomena of proto- 

 plasmic irritability and make direct attack upon this dominating conception, the 

 nrst formidable bulwark of vital territory. 



The following Papers were then read :— - 



1. The Influence of TAving Cells on the Transpiration Current. 

 By Professor H. H. Dixon, F.R.S. 



The resistance experienced in the passage of water through wood is considered 

 by some as necessitating the intervention of vital actions in the elevation of the 

 transpiration current in trees. According to Ewart a pressure of lO atmospheres 

 is required to raise water at the transpiration velocity in an elm-tree 18 m. high. 

 He allows that 3 atm. may be supplied by the traction exerted by the evaporat- 

 ing cells of the leaves, leaving 7 atm. for the living cells to supply, viz., 0'39 atm. 

 per metre of stem. Existing methods should easily reveal the presence of such a 

 force, but up to the present no such force has been detected. 



In order to reveal the presence of even a much smaller force of a vital nature, 

 if such exists, the following method was adopted : The rates of transmission 

 from above downwards of two similar branches were simultaneously observed. 

 To maintain both at the same temperature and so avoid differences in viscosity, 

 both were enclosed in the same water-jacket. One branch was then killed by 

 being surrounded with steam, and the rates of transmission again observed as 

 before. The similarity of behaviour of both branches showed that the influence 

 of the living cells on water-transmission is insensible. The experiment gives the 

 same result -when the branch is killed with picric acid. In the latter case, in 

 order to subject the two branches to conditions as similar as possible, water was 

 forced through the control while picric acid was forced through the experimental 

 branch. 



The fading of the leaves supported by killed branches has also been urged in 

 support of vital theories of the ascent of sap. It is, however, arbitrary to assume 

 that in this case the leaves fade directly owing to the want of water, or that the 

 methods of killing do not bring about changes in the sap and in the water-tracts 

 other than the destruction of the life of the cells. The fading of leaves due to 

 want of water is quite different from the fading of those supported by dead stems. 

 In the latter case the appearances indicate poisoning of the mesophyll-cells, while 

 in branches so killed, even if the trachece in the dead region itself escape being 

 clogged, those at higher levels in the stem and in the fading leaves ultimately 

 become plugged with reddish material. 



The poisonous effects of water which has passed through a killed branch may 

 be observed by supplying water to the basal leaves of a branch through its distal 

 part, after the latter has been steamed. Although provided with a two-fold 

 supply (viz., from the basal intact organs, and also through the killed upper part), 

 the leaves fade in a manner similar to those on a dead branch. 



It will be seen that the experiments described in the paper lend no support to 

 the vital theories of the ascent of sap. 



2. The Death-rate of Bacteria tinder the Action of Disinfectants, 

 By Miss Harriette Chick, D.Sc. 



Disinfection is shown to be a process exhibiting a close analogy with a chemical 

 reaction, the disinfectant representing one reagent and the protoplasm of the 

 bacterium the second. It is shown to be a gradual processs without any sudden 



