THE CLASSIFICATION OF THE BLACK OAKS. 



By WILLIAM TRELEASE. 

 {Read April 19, igi2.) 



(Plates X-XIII.) 



Since Alphonse de Candolle^ pointed out that the abortive ovules 

 occupy a definite position in a mature acorn, constantly basal or 

 nearly so in some species and as constantly apical or nearly so in 

 others, and crystallized the knowledge that the ripening of the fruit 

 occurs in one season in some and requires two seasons in others 

 (attending correspondingly retarded fertilization-) with as great 

 constancy,^ so many other correlations in wood, bark, leaf, stamens 

 and styles have been associated with these differences that the white 

 oak and black oak groups* have long been recognized as presenting a 

 natural division of our native species : the former with basal ovules, 

 short styles with dilated stigmas, usually annual often stalked fruit 

 essentially glabrous within and often with tuberculate or aristate 

 cupule-scales, leaf lobes not bristle-tipped, pale often flaky bark and 

 tough compact rather pale wood of slow growth ; the latter with 

 apical ovules, elongated slender styles, usually biennial nearly sessile 

 fruit tomentose within and rarely with tuberculate or tapered cupule- 

 scales, bristle-pointed leaf lobes, dark often deeply checked but not 

 flaking bark and darker wood of twice as rapid growth on the 

 average. 



The principal doubts as to the sufificiency of these group charac- 

 ters may be said to rest on an occasional easily understandable but 

 none-the-less misleading slip of the pen such as that of de Candolle's 



^A. de Candolle, Ann. Sci. Nat., Bot., IV., 18: 51. 1862. For various 

 other places of publication in French and English, reference may be made 

 to the catalogue of the Royal Society. 



* Conrad, Bot. Gac, 29 : 410. 1900. 

 *A. de Candolle, /. c, 50. 



* Engelmann, Trans. Acad. Sci. of St. Louis, 3: 374, 381, 388. 1876-7; 

 " Bot. Works," 390, 394, 397. 



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