ii ASCENT OF SAP IN STEMS 31 



was now melted and diluted till it set weakly at 13. At 

 a temperature of 30 to 40 this was supplied to the lower 

 end of the yew, the latter as before being kept warm 

 throughout its entire length by a water-jacket which was 

 never raised above 40. At the expiration of four hours 

 the liquid within the vacuous tube had risen by about 

 5 c.c. The experiment was then stopped, and the contents 

 of the tube tested with tannin. There was an opalescent 

 precipitate. Comparison with the solution below showed 

 that much of the gelatine had been held back by the wood. 



Starting the experiment a second time with the same 

 piece of yew, it transmitted 3*5 c.c. in four hours ; the 

 liquid drawn up affording this time a much denser preci- 

 pitate. A final test showed the wood to be still impervious 

 to air when a vacuum was maintained in the tube. 



A similar experiment with the wood of Pinus austriaca 

 gave a like result. It was observable that if the dilute 

 gelatine was not raised some few degrees above its melting- 

 point i.e., till the solution almost ceases to be opalescent 

 its passage was much less marked ; indeed in some 

 experiments only traces were transmitted through the wood. 

 This appears to be due to the fact that in solutions pre- 

 senting an opalescent or milky appearance, the gelatine is 

 probably still in the solid or gelatinous state ; the hetero- 

 geneous distribution and difference of refractive index 

 giving rise to the milky colour. In all cases a considerable 

 quantity of the gelatine is held back. One quantitative ex- 

 periment on Taxus gave the percentage of gelatine in the 

 transmitted liquid as only half that in the original solution. 



In one experiment the gelatine was stained with Klein- 

 enberg's hematoxylin. The solution was made of such 

 strength as to set at about 20, and was supplied at 40 to 

 the wood of Taxus baccata. It passed out colourless into 

 the glass tube, about 1 c.c. in two hours, the length of the 

 wood traversed being 2 5 cm., and its cross-section 22 

 sq. cm. This wood had not been treated with paraffin, 



