ii ASCENT OF SAP IN STEMS 37 



Generation of gas in the lumen. Bearing on 

 this same point the partial passage of water through 

 the walls the following experiments were carried out, 

 in which it was sought to replace the paraffin or 

 gelatine by a gas developed in the plant. Thus a cut 

 branch first supplied from a solution of tartaric acid and 

 subsequently from a solution of sodium bicarbonate will 

 have carbon dioxide evolved in the lumina of its conducting 

 tissues in consequence of the interaction of these substances. 



A preliminary experiment upon a lime branch (Tilia 

 microphylla) which had stood for two hours in a solution of 

 tartaric acid, and then one hour in sodium bicarbonate, 

 before finally being transferred to pure water, showed rapid 

 flagging of its leaves and soft shoots as the result. But 

 as this was possibly a direct consequence of the action of 

 the reagents, and not of the evolved gas, a more careful 

 experiment was carried out upon five branches of elm cut 

 from the same tree, with similar precautions, and, as far 

 as possible, of like dimensions. 



A and B were placed in sodium bicarbonate solution. 



C and D were placed in tartaric acid solution. 



E was placed in a solution of a mixture of tartaric acid 

 and sodium bicarbonate which had ceased effervescing. 



After 1 J hours A and C were interchanged in the solutions; 

 thus, in these two only was carbon dioxide developed. 

 B served as a control regarding the effects of sodium 

 bicarbonate alone, D, as a control for tartaric acid, E, for 

 the effect of the mixed solution without development of gas. 

 In five hours A and C were very much, and about equally, 

 flagged, while the rest remained fresh. Next morning, 

 however, all had drooped, showing that prolonged treat- 

 ment with either or both of these substances is injurious in 

 any case. It was evident, also, that the stoppage of the 

 lumina by the gas had greatly accelerated the flagging. 



It was not probable that the check upon aeration of 

 the tissues involved in all of the foregoing experiments 



