The American oaks / by William Trelease.

  • William Trelease
Date:
1924
Catalogue details

Licence: In copyright

Credit: The American oaks / by William Trelease. Source: Wellcome Collection.

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    [Vol. ridges in some tropical black oaks and a slighter but distinct manifestation of the same sort in our northern black oaks, may merit more attention than has been given it; and the other¬ wise aberrant live oak of our Gulf region has connate cotyledons, as Engelmann pointed out many years ago,—a character also ascribed to Q. arizonica by Sargent. Seedlings.—In the (frequently atavistic?) foliage of seedlings there is so much incon¬ stancy and so little relative comparability with mature foliage of the same species that it appears distracting to introduce the little that is actually and accurately known about oak seedlings into a monograph which aims primarily at making it possible to ascertain the proper names of the species in their adult form; but such studies are important in themselves, and it is possible that they may afford clues to relationship that are now lacking. ABNORMALITIES. TERATOLOGY. Apart from the heterophylly between the younger or infertile and the mature growth of many species and sometimes traceable between the successively unfolded leaves of a season’s growth, which is to be considered rather an indication of variability and which shows itself occasionally in persistent mutations like that of the heterophyllous white oak and the mani¬ fold horticultural forms of the species of northern Europe, few foliage monstrosities are found in this genus. The most noteworthy is a doubling of the blade, apparently of Q. Phellos, by which the Pleistocene Q. abnormalis is characterized. In flowers and fruit deviations from type appear to consist in variation, replacement or suppression of normal structures, etc., and a not infrequent occurrence of more than one seed in the acorn is attributable to the develop¬ ment of more than the customary one out of the six ovules normally present in an ovary. Exceptionally, an infertile pistillate flower is found elongated into a budlike body 15 or 20 mm. long, on which the usual cupule scales are imbricated. An unusual anomaly for what are considered lower Apetalae is the occurrence of two embryos within a single nucellus, reported by Harvey (Ann. Rept. Mich. Acad. Sci. vol. 19, p. 329, 1917.) GALLS. Few plants are so variously and so characteristically deformed by gall insects as are the oaks, and the constancy and symmetry of reaction of the tissues of the plant to the irritation of the insect furnish food for much reflection on the reasons for characteristic constancy in plant form. Perhaps the most striking of such deformities is that in which the galls simulate acorns in form and texture, e. g., in those occurring on the outside of the cup of certain of our white oaks noted by Engelmann and attributed by Riley to Cynips Quercus glandulus,3 and those developed from buds on some of the European oaks as a result of the attacks of C. fecundatrix. One specimen of the South American Quercus tolimensis at Dahlem shows a similar acornlike gall replacing an axillary bud. Because of their large tannin content, a number of the oak galls are of great economic importance. HYBRIDITY. Many observers have collected or reported what they have taken for hybrid oaks. In a few instances these do not appear to be more than extremes of one of the supposed parents, but most such specimens which I have examined seem to be of hybrid nature. It must be admitted that little actual evidence exists to support this opinion, which is based on their appearance. So far as my knowledge goes, no hybrids have been detected except between parents of a single subgenus,4 though supposed crosses of the aberrant red oak Q. Emoryi with the white oaks Q. grisea and Q. pungens are reported. Within the subgenera, crossing is usually between rather closely related species; but this is not always true, especially in the 3 This gall, among others, is figured by Felt in a comprehensive illustrated key to American insect galls (Bull. 200, N. Y. State Museum, in which oak galls occupy pp. 52-119.) «In contrast with this, Houba (ChSnes. p. 88) reports the red oak as grafted on English oak, and Hall gives an account of a supposed natural graft between alba and velutina.
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