6 EMORY OAK IN SOUTHERN ARIZONA. 



FOLIAGE. 



Although usually considered an evergreen, like the live oaks, 

 there may be times during the year when Emory oak is leafless. 

 Old trees are rarely without some leaves, but younger ones, up to 

 15 or 20 feet tall, may be bare for two or three weeks before the 

 new leaves appear, and, in dry seasons, even for a month or two. 

 During normal seasons Emory oak leafs in late April or early May, 

 but, in an abnormally dry year, may not leaf until June or early 

 July. There is a current opinion that all the old leaves are shed 

 just before the new crop appears; as a matter of fact trees begin 

 to shed their leaves in the fall, and continue to do so throughout the 

 winter and early spring. 



ROOT SYSTEM. 



Just as the form of the tree above ground is determined largely by the 

 site, so is the root system. The best developed roots are on the large 

 trees of the broad valleys, where the soil is deep, porous, and moder- 

 ately moist. They have well-developed tap roots and numerous 

 laterals within the first 2 feet beneath the surface. The laterals, like 

 the branches above, spread out in distinct planes, and at varying 

 distances from the stem, have sublaterals that go down at right angles 

 from 3 to 10 feet. The laterals that are close to the surface serve 

 two purposes: First, they secure proper aeration when the ground 

 is saturated; and, second, they are needed to anchor such large- 

 crowned trees. The tree has an overdeveloped, or hypertrophied, 

 root collar, because the present survivors are not of seedling growth. 

 Even with trees of undoubted seedling origin, repeated killing back, 

 either by fire, browsing animals, or frost and drought, make the final 

 trunk the survivor of many sprouts or sets of sprouts. 



Other marked characteristics of the root system are the intense 

 red color of the inner bark, the small proportion of root branching, 

 except near the root tips, and the strong development of mycorrhiza. 



GROWTH. 



It is comparatively easy to determine the growth of Emory oak, 

 because its annual rings are more distinct than those of other black 

 oaks of the region and much plainer than those of the white oaks. 

 Generally there is an abrupt formation of the large thick-walled 

 vessels in spring, though on poor sites, or as the result of abnormal 

 seasons, the annual character of the rings may not be readily deter- 

 mined. Sometimes, as in seasons of more than one distinct growth 

 period, with a time of comparative vegetative rest between, there will 

 be false rings, though these are rare. 



Even on the same site growth may vary with individual trees or 

 groups of trees, and slightly better soil-moisture conditions in iso- 



