37§ TRANS. ST. LOUIS ACAD. SCIENCE. 



sessile, or rarely (and that sometimes in the same species) borne 

 on short, more or less erect, styles ; in the Black-oaks we always 

 find them on longer, patulous, or recurved styles * As the stig- 

 mas are measurably persistent, we often recognize this difference 

 even in the mature fruit. 



The fruit exhibits the most important characters in the period 

 of its maturation, first noticed by Michaux, and especially in the 

 position of the abortive ovules, the beautiful discovery of A. De 

 Candolle. But before I speak of these I must allude to the 

 position of the fruit on the branch. It is single or clustered 

 in the axils of the leaves or their scars, sessile, or more or less 

 peduncled. In the Black-oaks the peduncle is short or missing, 

 but in the White-oaks it is sometimes several inches in length ; 

 its presence, however, is of very little specific value, as in many 

 species either sessile or peduncled acorns are found. In some oaks 

 this feature is connected, with slight differences, in the length of 

 the petiole, or the shape of the leaf; the distinction between the 

 European J^. Robur and j^. pedunculata is based on such dif- 

 ferences, and we have an analogous difference in our j|>. alba, 

 where, at least here in the Mississippi Valley, the form with 

 deeply pinnatifid leaves has usually peduncles as long or little 

 shorter than the acorn, and the other form with more broadlv- 

 lobed leaves has shorter peduncles or sessile fruit ; but sometimes 

 we find sessile and peduncled fruit on the same tree. Some 

 White-oaks have always sessile or nearly sessile acorns, as j£>. 

 stellata, while Q. bicolor always bears them on long peduncles. 



The acorns mature either in one season or in two, and gener- 

 ally speaking we find the annual maturation among the White- 

 oaks and the biennial maturation in the Black-oaks, but the ex- 

 ceptions to this rule prove that this peculiarity is not necessarily 

 connected with the essential characters of the two groups. We 

 have one western White-oak, Q. chrysolepis,\\\\.b. biennial fruit, 

 and three Black-oaks with annual maturation, ^. pumila of the 

 east, and J^>. agrifolia and J^. hypoleuca of the west. 



The biennial maturation is easily recognized in the oaks with 

 deciduous leaves ; the tree is never without younger or older fruit, 



* A group of White-oaks with biennial fructification, peculiar to Southern Europe and 

 Eastern Asia, the best known representatives of which are jg. Cms. j§| Pseudo-Suber, and 

 jg. occidentalis, differs from all these by their patulous or recurved styles bearing ligulate. 

 acutish stigmas. 



