64 TIMBER AND SOME OF ITS DISEASES. [CHAP. 



in 1 879 that if a transpiring branch is cut under water, 

 the air presses the water with considerable rapidity 

 into the vessels. 



So much by way of introduction. I now propose 

 to start with the position of affairs in 1882, the 

 year in which Sachs's Vorlesungen iiber Pflanzen- 

 physiologie first appeared. 



At this time it was allowed by all that the water which 

 ascends the stem of the tree passes from the roots to 

 the leaves in the wood that it is absorbed by the 

 root-hairs, traverses the roots to the stem, and passes 

 up the wood to the leaves, whence it passes off by 

 transpiration. It was also agreed that the main flow 

 takes place in the " sap-wood " (alburnum), because 

 the simple experiment of " ringing " the stem proved 

 that with most trees the flow is seriously diminished, 

 or stopped, if the outer wood is removed as well as the 

 cortex, whereas no harm ensues if the alburnum is 

 left intact : moreover, observations on hollow trees 

 showed that the inner parts of the timber are not 

 necessary to the ascent of the water. 



Further points of agreement were found in the 

 knowledge of the structure of wood the annual rings, 

 medullary rays, the differences between duramen and 

 alburnum, the properties of the cambium, &c. It 

 was also known that while the secondary wood of 



