76 Proceedings of the Ohio State Academy of Science 



of high trees is not fully understood. In early spring, as in the 

 sugar maple, the water accumulates in the sap wood since there 

 are no leaves from which it can be thrown off above. 



The crown is a system of branches on which the leaves are 

 developed and exposed to ths 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 col- 

 oring matter is called. Another important function of the leaves 

 is the transpiration of the surplus water brought 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 or- 

 gans, although not exclusively 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 

 tj^pes. If the main trunk of a tree extends upward through the 

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

 Austrian pine. \\'hen the terminal bud 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. Ex- 

 current trees are often spire-shaped like the Norway spruce; 

 while deliquescent stems commonly give rise to dome-shaped 

 crowns, as in the white elm. If the terminal bud withers or is 

 self -pruned, as in the linden, the branching is sympodial. If the 

 leaves are opposite and the two lateral end buds develop, the ter- 

 minal bud being" self-pruned, the result is a sympodial dichotomy, 

 as in the bladdernut. Trees in which the terminal buds are per- 

 sistent 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 place only a single ring 

 is produced each year. Each ring usually consists of two layers 

 called early wood and late wood. During special seasons or if 

 growth is checked at times during the growing period more than 

 one ring may be produced, although this is never perfect and 



