Vascular differentiation in the wheat embryo

Abstract

The sequence of vascular differentiation in the scutellum, coleoptile, and firbt foliage leaf of the wheat embryo is traced by examining serial sections of these organs at selected intervals after the initial soaking of the grain. Mature sieve elements are found first in the scutellum 3-6 hr after soaking, in the midrib of the first leaf after 6 hr, and in the coleoptile after 18 hr. In all three organs xylem differentation lags behind that of the phloem; mature tracheary elements are present in the scutellum by 18 hr, in the midrib by 24 hr, and in the coleoptile by 30 hr. It is suggested that there are four loci of sieve element differentiation and two loci of tracheary element differentiation. These observations are discussed with reference to previous accounts of vascular differentiation.