MOTION OF THE JUICES. 



381 



Fig. 66. 



for growth, as in moist, warm 

 air, with its lower extremity 

 in water, roots form chiefly 

 at the edge of the bark just 

 above the removed ring. The 

 twisting, or half-breaking, as 

 well as ringing of a layer, 

 promotes the development of 

 roots. Latent buds are often 

 called forth on the stems of 

 fruit trees, and branches grow 

 more vigorously, by making 

 a transverse incision through 

 the bark just below the point 

 of their issue. Girdling a 

 fruit-bearing branch of the 

 grape-vine near its junction 

 with the older wood has the 

 effect of greatly enlarging the 

 fruit. It is well known that 

 a wide wound made on the 

 stem of a tree heals up by the 

 formation of new wood, and 

 commonly the growth is most 

 rapid and abundant above the 

 cut. From these facts it was 

 concluded that sap descends 

 in the bark, and, not being 

 able to pass below a wound, 

 leads to the organization of 

 new roots or wood just above 

 it. 



The accompanying illustration, 

 Fig. 66, represents the base of a cut- 

 ting from an exogenous stem (pear 

 or currant), girdled at />' and kept 

 for some days immersed in water to 

 the depth indicated by the line L. 



