37^ TRANS. ST. LOUIS ACAD. SCIENCE. 



lata of the first, and J^. nigra of the second group, both with 

 densely tomentose, thick, young leaves. In other oaks, mostly 

 such as have broader and more or less entire leaves, the young 

 leaves imbricatively cover one another like those last mentioned, 

 but are convex on the upper side, with the edges turned down or 

 back. Such is the case in ^>. cinerea, myrtifolia, agrifolia, 

 aquatica, chrysolepis, and, I believe, also in J^. undulata, and 

 in <*£>. Wislizeni ; I find the same to be the case in the deeplv 

 lobed Q.falcata. 



The narrow-leaved oaks of both sections have revolute young 

 leaves, the halves being spirally rolled backwards towards the 

 midrib, so that only the upper side of the leaf is exposed ; the 

 point of the young leaf is somewhat spreading so that the branch- 

 let has a squarrose appearance, while in those with imbricative 

 vernation it is compact. I find the revolute leaf in j^>. virens, 

 pumila, Phellos, heterophylla, and imbricaria. In J^>. Catesbcei 

 I observe an inflexed vernation, the long bristle-pointed lobes of 

 the nascent leaf being curved down over the still younger one. 



I believe that the characters of vernation will not only help to 

 distinguish allied species or doubtful varieties, but will also assist 

 in unravelling the intricate questions of hybridity. 



The young leaves of almost every oak are coated with a dense 

 stellate down, which in some (Q. alba, rubra, etc.) is early de- 

 ciduous, or it disappears later, or is entirely persistent. Besides 

 these stellate one-celled hairs, several species, those with a clam- 

 my feeling of the young leaf, have another kind of hair, single -or 

 a few stellately connected, consisting of several cells, obtuse or 

 clavate, sometimes branched, and often colored, apparently glan- 

 dular. I notice these articulate hairs, among the White-oaks, in 

 <^>. stellata, and less conspicuously in ^. macrocarpa ; among 

 the Black-oaks, in .Q. nigra, myrtifolia, cinerea, falcata, 

 aquatica, and laurifolia ; in Q. chrysolepis the characteristic 

 "golden scales" are no scales, but consist entirely of such articu- 

 lated yellow hair, and the young Q. Catesbcei has the same rusty 

 coating. 



The venation and more or less distinct reticulation of the 

 leaves also present characters not to be neglected ; by them, e.g. 

 two easily confounded Californian oaks, J^>. agrifolia and Wisli- 

 zeni can readily be distinguished even in sterile branchlets. 



