62 TRANSPIRATION AND ASCENT OF SAP ch. 



that which was centrifuged some days after steaming 

 is called "steamed indirect"; while the liquid obtained 

 from the steamed branches which had been emptied 

 of their sap, and subsequently filled with water, is 

 tabulated as ' steamed indirect + water." The ciphers 

 in the table indicate that no effect was observable on that 

 day of the experiment under which the figure is placed, 

 while a plus mark shows that an effect was observed. 

 Query-marks indicate that only some of the leaves tested 

 were affected, or that only slight protoplasmic contraction 

 was observable. In each case three or four leaves were 

 immersed in the liquid and examined. 



It may be noted that, in the case of Cotoneaster frigida, 

 Syringa vulgaris, and Ilex aquifolium (see footnote, p. 61), the 

 liquid centrifuged from the steamed branch, 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 suffi- 

 ciently 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 experi- 

 ments probably affords an explanation of the fact that, 

 even when steamed branches are washed out immediately 

 after the heating, as described later, some of the leaves 

 above perish from poisoning. 



But it is possible to demonstrate the poisonous action 

 of the substances liberated in the killed portions of branches 

 on their own leaves without at the same time curtailing 

 their water supply in any way. This was found 

 feasible in the following manner : One branch of 

 a bifurcated shoot of Syringa vulgaris was killed by 

 immersion in water at about 90 C. for ten minutes. 

 After this the dead branch was stripped of its leaves, and 



