44 FIEST STUDIES IN PLANT LIFE 



8. How a tree ringed halfway round behaves. 



You will now be able to see how it is that a tree may 

 live for a long time after it has lost its heartwood and 

 become hollow. You will also be able to see how it is 

 that a tree may live on, after part of the bark has 

 been removed. The tree dies, of course, if the bark 

 be removed all round the tree ; but if even a narrow 

 path be left for the sap-tubes, the tree can often keep 

 some of the branches in healthy leaf. On the footpath 

 that runs beside the railway line from Jolimont to 

 Eichmond, there is a gum tree bearing this inscription : 

 " A bark canoe was cut from this tree by the wild 

 blacks prior to the arrival of the white man." At the 

 top and bottom the marks of the stone tomahawk are 

 stiU visible. The bark that was left was sufficient to 

 keep the tree alive, and it bears leaves to this day. The 

 rush of healing sap has made the edges of the wound 

 fold over in the usual way. You can see how those 

 edges reached out in the vain attempt to bridge over 

 the gap and how they finally fell back on the hving 

 part of the tree, leaving the hard, dead heartwood 

 exposed to the air. It is probably more than a 

 century since this happened ; and to-day the hard 

 dead heartwood looks as little a part of the tree as if 

 it were a great stake of dead wood fixed for the 

 support of the part that is still alive. 

 Questions and Exercises. — 



(1) To show the water-path in the stem, make experiments with 

 garden halsam, geranium, and bleached celery. 



Note. — In the balsam the red sap-tubes can be seen through the 

 thin bark. 



(2) How is it that a hollow tree may stand for many yeai-s if 

 only it has strength enough to stand against the wind ? 



(3) Look in the annual rings of an old tree foi- the old root-sap 

 tubes — no longer used. The tubes look like pores. 



