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HISTOLOGICAL STUDIES ON THE COLEOPTILE. II. COMPARATIVE VASCULAR ANATOMY OF COLEOPTILES OF AVENA AND TRITICUM
Author(s) -
Thimann Kenneth V.,
O'Brien Terence P.
Publication year - 1965
Publication title -
american journal of botany
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.218
H-Index - 151
eISSN - 1537-2197
pISSN - 0002-9122
DOI - 10.1002/j.1537-2197.1965.tb07266.x
Subject(s) - coleoptile , avena , xylem , biology , endosperm , botany , avena fatua , vascular bundle , caryopsis , germination , vascular tissue , anatomy
The vascular bundles in the uppermost 1‐4 mm of the coleoptiles of 9 varieties of Avena sativa , and also of Avena fatua L., all terminate essentially vertically with a small “cap” of tracheary elements. In Triticum vulgare Vill., by contrast, they terminate with a horizontal or downward‐pointing section. This brings the two bundles more or less together and may result in their complete fusion, usually with a short vascular extension. In both genera the bundles contain one or more series of apparently active, undifferentiated cells. In the mature embryos the bundles are entirely procambial in nature, but xylem differentiation begins rapidly upon germination and proceeds towards the tip, which is reached by the time the coleoptile is 1.5 mm long; thereafter it proceeds basipetally and it may continue at the base after elongation has ceased there. The differentiation of stomata also appears to proceed basipetally. It may be deduced that the coleoptile cannot form lignin while in the embryo but begins to do so upon germination. Parallels are brought out between auxin production first by the endosperm and then by the tip, on the one hand, and lignification in the xylem and in the stomata, on the other.