374 TRANS. ST. LOUIS ACAD. SCIENCE. 



dance of material must shake our confidence in our discrimina- 

 tion : within the compass of a few hundred yards we find not 

 only the forms above distinguished, but numbers of others which 

 are neither the one nor the other, but which are intermediate 

 between them and clearly unite them all as forms of one single 

 extremely polymorphous species. 



If one oak behaves thus, why not others ? Thrown into a sea 

 of doubt, what can guide us to a correct knowledge ? 



Though oaks are so common and such well-studied plants, I 

 venture in the following pages to repeat old observations in order 

 to combine with them some which I think are new, and which 

 will help to throw a little more light on the subject. 



The trunk — its bark as well as its wood — is what we first 

 contemplate, and this at once takes us to one of the principal 

 points I wish to discuss. 



That the trunk is that of a large, sometimes one of the largest, 

 or of a middle-sized tree, or occasionally that of a shrub, even a 

 very low one, is well known. On the Atlantic slope of the con- 

 tinent most species of oaks make trees and only a few are known 

 as shrubs ; I can now recall not more than one species, the live- 

 oak of the south, which occurs in both forms : usually an im- 

 mense tree, it occasionally bears a rich harvest of fruit as one of 

 the smallest bushes. But it is different on the Pacific slope ; 

 there we find many oaks as trees in the lower countries, and as 

 shrubs, usually with smaller foliage and smaller fruit, in the moun- 

 tains. The lesser number of oaks seem to occur solely in one or 

 in the other of these forms. 



Examining the bark, we at once become aware of the fact 

 that the popular distinction of "White-oaks" and "Black oaks" is 

 based on correct observation. The paler, ashy-gray bark of the 

 former and the darker, often nearly black, color of the latter cor- 

 responds, as will be shown, with other essential characters, and 

 well marks the two principal groups of our Ameiican Oaks. The 

 bark of the White-oaks is inclined to be scaly or flaky, that of the 

 Black-oaks is usually rougher and deeply cracked and furrowed. 



The -wood of the White-oaks is tougher, heavier, and more com- 

 pact — the only wood which is fit to be used by the wheelwright 

 or cooper, and is for their purposes unsurpassed. The wood of 



