59 



<c/ Bark, 



(1) Birch bark peels in thin horizontal layers. 



(2) Ash bark opens in many irregular netted cracks near 



each other. 



(3) Chestnut bark opens in longitudinal cracks quite 



distant from each other. 



(d) Wood. 



(1) Heart- wood dead, dark, central wood. 



(2) Sap-wood carries sap in growing season. 



(3) Medullary rays silver grain. 



(4) Annual layers minute tubes or cells. Large in early 



growing season; small in late growing season. 



(5) Age of tree generally told by annual layers. 



(e) Branches. 



(1) Opposite leaves, generally opposite branches. 



(2) Alternate leaves, always alternate branches. 



(3) Erect, horizontal and drooping Lombardy poplar, pine 



and weeping willow. 



(f) Buds. 



I. As to Position. 



(1) Terminal at end of twig. 



(2) Lateral along sides of twig. 



(a) Axillary, in the leaf axil. 



(b) Accessory, buds clustered around axillary buds. 



(c) Adventitious, buds produced irregularly. 

 Nodes points on stem at which buds are pro- 

 duced. 



Internodes spaces between nodes. 

 II. As to Activity. 



(1) Active those that develop. t 



(2) Dormant those that form but do not develop. 



III. As to Covering. 



(1) Scaly covered with dry, tough, bark-like layers. 



(2) Naked without scaly covering. 



(3) Hidden those buried under or in bark. 



IV. As to Arrangement. 



(1) Opposite two at same node and opposite. 



(2) Whorled three or more arranged around the same 



node. 



(3) Alternate in ranks around stem not being opposite 



or whorled. 

 (g) Leaves lungs of plants. 



(1) Arrangement alternate poplar; opposite maple; 

 clustered pines ; scattered spruce. 



