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tlu' wood. liowevtT. are called wood vessels. Just how the 

 water is able to pass up to the tops of high trees is uot i'ull.\ 

 understood. in early spring, as in the sugar maple, tlie 

 water accumulates in the sap wood since there are no leaves 

 from which it can he thrown off above. 



1 he crown is a system of branches on which the leaves 

 are developed and exposed to the light. In the leaves most 

 of the food is manufactured which the tree uses for its 

 growth and nourishment. This production of organic food 

 is carried on through the agency of sunlight and chlorophyll, 

 as the green coloring matter is called. Another important 

 function of the leaves is the transpiration of the surplus 

 water brouglit up from below. The water transpired by a 

 large tree in a single day is often very great in amount. The 

 leaves are also important breathing organs, although not ex- 

 clusively so ; for all the living cells in the entire plant carry 

 on the process of respiration. 



The system of branching in the crown may be of various 

 types. If the main trunk of a tree extends upward througli 

 the crown to the tip it is said to be excurreht, as in the larch 

 and Austrian pine. When the terminal Imd has no pre- 

 eminence over others and the main trunk is soon lost, the tree 

 is round-topped or spreading and is said to be deliquescent, 

 as in the apple. Excurrent trees are often spire-shaped like 

 the Norway spruce; while deliquescent stems commonly give 

 rise to dome-shaped crowns, as in the wdiite elm. If the 

 terminal bud withers or is self-pruned, as in the linden, the 

 branching is sympodial. If the leaves are opposite and tiie 

 two lateral end l)uds develop, the terminal bud being self- 

 l)runed. the result is a sympodial dichotoni}-, as in the 1)lad- 

 dernut. Trees in wdiich the terminal buds are persistent and 

 functional are said to have a monopodial system of branching. 



The trunk or any branch of a coniferous or dicotylous 

 tree consists of four main parts, the pith, the wood, the 

 cambium or growing layer, and the bark. The wood consists 

 of a series of annual rings, since if normal growth takes 

 j)lace only a single ring is produced each year. Each ring 

 usually consists of two layers called early wood and late 

 V. ood. During special seasons or if growth is checked at 

 times during tlie growing period nmre than one ring may be 

 l»roduced, although thi.s is ncxcr perfect and l-an usually be 



