ENGELMANN — OAKS OF THE UNITED STATES. 375 



the Black-oaks is brittle and porous, makes poorer firewood, and, 

 made into barrels, holds only dry substances. Undoubtedly the 

 microscopical investigation of both classes of oak-wood will sci- 

 entifically establish and confirm these distinctions. 



While many other trees, such as Pines, Walnuts, Hickories, 

 Gleditschia, etc., grow rapidly in the first decades of their life, 

 and make narrower and narrower annual rings as they grow old- 

 er, the oaks either hold their own, the annual rings being as wide 

 in age as they are in youth, or they grow more rapidly after the 

 first 50 or 100, or even 150 years of their existence. 



The winter-buds., especially the terminal ones, show some cha- 

 racteristic differences ; they are larger or smaller, acute or obtuse, 

 smoothish or hairy or tomentose ; ^uercus Garryana can be 

 readily distinguished from all the allied Californian oaks by its 

 large, pointed, tomentose winter-buds. 



In the LEAVES, so extremely variable in form, certain types are 

 generally recognized. It is not here the place to expatiate on 

 these well-known topics ; but I may be allowed the observation, 

 that those oaks, which in the perfect state have deeply-lobed or 

 pinnatifid leaves, show in young shoots or on adventitious branch- 

 lets less divided or only dentate, sinuate, or even entire leaves 

 (e.g. ^. alba^ stellata^ falcata.^ coccinea^ palustris^ etc.), while, 

 singularly enough, the oaks whose leaves in the adult tree are 

 entire or nearlv so, often have on the young shoots dentate or 

 lobed leaves. I need for examples only refer to ^. aquatica^ J^. 

 Phellos^ and J^. virens : and even ^. nigra belongs here. 



The vernation of the oak leaves has sometimes been mentioned 

 as conduplicate, meaning that the upper sides of both halves of the 

 nascent leaf are applied together, and this really is the case with 

 most oaks which I have been able to examine in this early stage. 

 We find it both in White and Black-oaks — almost always, I be- 

 lieve, in those with broad and deeply-lobed leaves ; I mention 

 only c^. alba^ macrocarpa and Garryana, ^. coccinea and fa- 

 lustris, and also the forms allied to ^. Prinus, even those with 

 narrower, dentate leaves. In the more deeply-lobed, broad-leaved 

 Black-oaks the two halves of the leaf are, besides, plicate parallel 

 with the principal nerves. 



Next to these range the oaks with the young leaves concave 

 -and imbricately covering one another. Such we find in ^. stel- 



