1905-1906.] 429 



by excreting an acid substance. As the root descended into 

 the soil, SO' the stem rose into the air, giving off branches bear- 

 ing a number of leaves. 



The cross-cut end of an oak log was described, showing 

 the pith, heartwood, sapwood, and the delicate sheath 

 called the cambium, situated outside the outermost ring of 

 sapwood, followed by a jacket of bark, the innermost layers 

 being known as bast. Piercing the wood and bast were a 

 number of radiating lines, called medullary rays. Among 

 these parts the cambium sheath is the most important, and 

 covers the root, trunk, branches, and twigs like a huge glove. 

 Its importance lies in the fact that without it there would be no 

 new wood or bast. Turning to one of the rings in the oak-log, 

 reference was made tO' the large porous tissue formed in the 

 spring, followed later in the season by a dense woody mass, 

 called the summer wood. It was for this reason that rings 

 were so clearly marked on the ends of many logs, and as it is 

 usual for one to be formed annually, they are called annual rings. 

 Woods with large pores produced an open grain, while closely- 

 deposited wood produced a close grain, but the user of timber 

 required wood and not cavities, and the fewer cavities there are, 

 the better the wood when used as timber. It is a closely- 

 packed, thick-walled tissue that is needed. 



Reference was made to the heartwood as a dead tissue 

 formed from the living sapwood, and that as the sapwood 

 changed into heartwood it becomes impregnated with all kinds 

 of antiseptic substances, to the nature of which heartwood owes 

 its durability. In the willow the heartwood does not change 

 its colour, and the protective substances were absent. This 

 accounted for so many hollow willow trunks to be seen on a 

 country walk, and which proved that heartwood is not neces- 

 sary for the life of a tree, as can be witnessed during the 

 summer, when hollow willow trunks will be found bearing a 

 crop of leaves, and shewing every sign of a healthy life, because 

 the sapwood of trees performs the function of conducting the 

 crude sap up the trunk to the leaves. Some woods never 

 possess heartwood, but in such as have it the more heartwood 



