388 
AMERICAN JOURNAL OF BOTANY 
[Vol 8 
which the presence of one style in this order has prompted eadier students 
of taxonomy to infer the presence of but one carpel; internal anatomical 
study, however, reveals the unquestioned presence of two carpels. 
Material 
The flowers in this study were killed in chrom-acetic acid, embedded in 
paraffin in the usual way, and sectioned serially, the sections being eight 
and ten microns thick. Because the flowers are very small and ephemeral 
the vascular supply is very delicate and not readily differentiated. Experi- 
mentation with various stains proved the safranin and light green combina- 
tion to be the most practical. 
Ulmaceae 
Ulmus. The species of this genus have flowers arranged in the inflo- 
rescence in a graded series from a short, slender, raceme-like cluster or a 
loose panicle-fascicle, with slender, jointed pedicels as in Ulmus americana 
and U. racemosa, to a very much reduced fascicle with pedicels practically 
eliminated as in U.ftdva, U. scahra, and U. campestris. Taxonomists state, 
usually, that the flowers are simple with bell-shaped perianth, which is 
9- to 4-lobed, imbricated, stamens opposite to, and of the same number as, 
the lobes, hypogynous, inserted at the base of the perianth; pistil of two 
carpels, each with a style, one loculus with a pendulous anatropous ovule. 
The one-whorled perianth of Ulmus can be called neither sepaloid nor 
petaloid; it is succulent to membranous-scarious with little or no chloro- 
phyll, possessing stomata equally distributed over its outer surface. 
Ulmus americana L. has a flower (PI. XV, fig. i) which posseSvSes a 
perianth of 8 lobes, three lateral right and three left, one posterior, and one 
anterior. Each lobe is accompanied by a stamen. Figure i shows the ir- 
regular character of the flower. This is a feature usually ignored. Lindley 
(13) mentions this condition; Britton, in his manual of the northeastern 
states and Canada describes it as "calyx oblique." This zygomorphy is 
evident in all the elms studied. Flowers sectioned in transverse planes from 
the pedicel to the distal end show that the vascular supply to the posterior 
organs usually passes off from the stele before that of the anterior organs. 
Such series of sections followed through numerous flowers of U. americana 
reveal the following facts. 
The pedicel in all species of Ulmus has an ectophloic siphonostele in the 
form of a more or less continuous cylinder (PI. XV, fig. 5). The first break 
in the stele is on the posterior side where a wide trace passes off leaving a gap 
in the cylinder. As nearly simultaneously with the break as can be appre- 
ciated, there separates from the inner face of this trace a portion composed 
of one or two vessels (fig. 6, m, n). The outer bundle is destined to pavSs to 
the posterior perianth lobe, and the inner to the accompanying stamen. 
Fifty microns above this section (fig. 6), the outer strand divides radially 
