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When the leaves sprout afresh in the spring on trees that have lain dormant 

 or shed their leaves in the winter, there is a great demand by the trees for water, 

 and the pipes and cells which are then formed have thin walls and large open- 

 ings. Later on, in summer, there is not so much want of water, and smaller 

 openings will do; at the same time the bark begins to press on the wood, so that 

 the cell walls must be capable of resisting this pressure. Therefore in summer 

 the pipes have thick walls and small openings. In winter growth stops, as has 

 been said, and it begins again next spring with the pipes with large openings. 

 These being formed next to the thick-walled ones give the appearance of a ring 

 when the wood is cut across. 



Running across the annual rings from the centre of the tree to the bark 

 there are some thin lines. These are called the medullary rays, and to them 

 mainly is due the figure possessed by many woods. In order to see these 

 medullary rays at their best, one has to cut the wood in a particular way, that 

 is, along a radius, or as the timber man says "on the quarter." The breadth of 

 the rays varies in different species of trees, being difficult to see in eucalypts 

 and pines, but in some others, such as Casuarinas, ^heoaks and Banksias, standing 

 out quite clearly. These medullary rays consist chiefly of soft cells which 

 keep up a connection through the harder timber from the centre of the tree to 

 the bark. They, as well as some other parts, are used by the tree as storehouses 

 for any excess of starch that may be in the food, and, it is believed, are concerned 

 in the series of changes whereby sapwood is ultimately converted into heart- 

 wood. 



Reproduction. — Nature makes plentiful provision for the preservation of 

 tree growth. All trees when they come to maturity bear flowers, although some- 

 times these are not very conspicuous. These flowers in due time develop into 

 fruit and seeds, which fall to the ground and give birth to new trees. Besides 

 reproduction by means of seeds, many trees are able to spring up again by means 

 of shoots from the stump after the tree has been cut down, or by suckers from the 

 roots. This power varies in the different species, and upon it depends the pro- 

 duction of coppice woods, about which something will be said when we come to 

 speak of forests. 



