Development of the Vascular System in the Fertile Floret of Anthoxanthum odoratum L. (Gramineae). I. Traces to the Fertile Lemma and Palea

Abstract

Development of the vascular system to the lemma and palea in the rachilla of the fertile floret of Anthoxanthum has been described. In the earliest stage, procambia for the median (M), rightmost (RR), and leftmost (LL) traces to the lemma were continuous with rachilla bundles 3 (anterior), 2, and 1 (posterior), respectively. Procambium for the palea trace (P) was continuous with bundle 1 or 2. Procambia for the lemma traces immediately to the right (R) and left (L) of M arose in isolation and differentiated bidirectionally. In later stages, L and R were most frequently continuous with bundles 1 and 2, respectively. Throughout later stages, procambia for LL, RR, and M were consistently continuous with bundles 1, 2, and 3 in the same pattern as in the first stage. Procambium for P varied in its relationship with the two posterior bundles. Whether procambia for traces M, P, RR, and LL develop acropetally and continuously from the rachilla bundles or in isolation could not be determined from the stages examined. However, the variation in the relationship of procambial P to bundles 1 and 2 may reflect its isolated initiation. Sieve elements were first initiated for M, then for P, L, and R, and lastly for LL and RR. The first observed immature sieve elements of M were contiguous with mature sieve elements of bundle 3 but were not continuous via sieve plates within the region examined. Similarly, the first observed immature sieve elements of P contacted mature sieve elements of bundle 1 but also were not continuous via sieve plates. Sieve elements of LL and RR were first observed as continuous with sieve elements of bundles 1 and 2. Whether sieve elements of M, P, LL, and RR developed continuously and acropetally from the bundles at the floret base or in isolation could not be determined from the stages examined. However, the isolated initiation of both procambia and sieve elements for L and R indicates that procambia and protophloem of the other laterals of the lemma also arose in isolation. Furthermore, no sieve plates link the immature sieve elements of M or P with mature sieve elements of bundle 3 or 1, again indicating that the former traces arose in isolation. Tracheary elements usually differentiated after the sieve elements from the procambial traces near their attachment to the rachilla bundles.