30 TRANSPIRATION AND ASCENT OF SAP ch. 



water. A length of 10 cm., straight and free from side 

 branches, was cut from a branch of Taxus baccata, the mean 

 diameter being 25 cm. This was deprived of its bark, and 

 affixed by an india-rubber ring at one end to a glass tube 

 communicating with an air-pump ; a little water in the 



tube covered the upper end of the 

 wood. (Fig. 4 shows the arrange- 

 ments.) On exhausting the tube, 

 bubbles rose from the surface of 

 the wood. These could be stopped 

 by simply immersing the lower 

 end in mercury. Hence it was 

 concluded that continuous air- 

 passages existed in this piece of 

 wood, which should be stopped 

 before any tests could be made 

 as to its permeability by gelatine. 

 Accordingly the lower end was 

 dipped in melted paraffin at about 

 70 C, the melting point of the paraffin being 56, and the 

 whole length of the stick jacketed by water which was 

 maintained at 70 for 45 minutes, a vacuum being pre- 

 served in the tube attached to its upper end during this 

 time. Finally the stick was cooled slowly from above 

 downwards by lowering the water-bath to allow of the con- 

 traction of the paraffin being made good by supply from 

 below. When all was cold, the end was pared to expose 

 lumina free from paraffin. The stick now drew up water 

 freely, 3 or 4 c.c. in 15 minutes, but allowed neither air 

 nor mercury to pass up. The water pumped through was 

 next tested by a solution of tannin, but remained perfectly 

 clear. We conclude therefore that no direct air-passages 

 remain open, and that nothing is yielded by the wood of 

 the yew giving an obscuring reaction with tannin. 



Some gelatine which had been cut up into fine threads 

 and soaked in repeatedly changed water for two days 



Fig. 4. 



