24 



part has been hitherto divided by physio- 

 logists into two parts, the iieart wood or 

 dead wood, and the alburnum or unripe, 

 and outside rings, or latest deposits of 

 wood around the stem. It was considered 

 that the heart wood really was dead 

 wood, and that the upward course of the 

 sap was through the alburnum, or latest 

 rings of wood only. In March 1832 I 

 remarked the stems of some birch trees, 

 which I had cut down in the previous 

 November, bleeding from the heart wood. 

 I was not then aware that Coulon had 

 about this time observed the same thing 

 in cutting down some poplar trees in 

 France. I afterwards satisfied mj^self, in 

 various ways, that the whole of the wood 

 is the conduit for the upward course of 

 the sap. 



In April 1832 I found a birch tree in 

 Dyhrram Park, of from sixty to seventy 

 years growth, which had a large scar 

 from injuries from cart-wheels. The 



