406 AMERICAN JOURNAL OF BOTANY [Vol. 8 
plexus from which also descended the Ranalian line. The Urticales have 
advanced parallel with the Ranalian stock to a high degree of specialization, 
namely, zygomorphy. Accompanying this specialization, or following it, 
the Urticales show great reduction in all parts of the flower. The result 
has been a group of plants combining characters belonging to primitive 
and to recent types, a combination which makes them a generalized rather 
than a specialized group from which no descendants seem to hr ve arisen. 
Summary and Conclusions 
1. The anatomy of the flowers of the Urticales reveals a number of 
features extending throughout the order, which are not appreciable from a 
macroscopic investigation. 
a. Ulmus, the primitive genus, shows evidence of suppression of a 
whorl of stamens and of one of perianth parts. The existing stamens 
are fused with the gamophyllous perianth. The parts of these whorls 
are somewhat spiral in arrangement and very inconstant in number. 
h. The bicarpellate condition has been derived from a polycarpellate 
condition as evidenced by the presence of vascular supply to suppressed 
carpels. Also, vestigial bundles indicate that the bicarpellate gynoe- 
cium is becoming unicarpellate by the suppression of one carpel. 
c. The perianth parts are reduced in number by abortion, suppres- 
sion, and fusion ; in some cases the inner whorl has entirely disappeared, 
in others vestiges of its vascular supply remain. In some forms the 
inner and outer whorls are fused and occur as one whorl. 
d. Zygomorphy is a conspicuous character of all species studied; 
evidence of it is not only found externally but appears also on micro- 
scopic study of transverse sections of the flowers. 
e. Palmate venation, if no longer present in the foliage, is still 
present in the perianth parts in some forms. 
/. The ovules are foliar organs. The orthotropous ovule in the 
higher members of the order has come to its basal, erect position by 
a sinking from an apical or lateral position of the anatropous ovule in 
the primitive members. The "cauline" ovule in the Urticales is 
apparently such due to reduction. All "cauline" ovules may possibly 
be simply the result of the same process. 
g. The vascular supply to the uniovulate ovary suggests a poly- 
ovulate ancestry. 
h. Accompanying coalescence and adnation, the flowers have been 
greatly reduced in all floral organs. 
2. In plant organs suffering reduction the vascular system disappears 
in advance of the organs, or persists as abortive bundles after the organs 
have disappeared. 
3. The combination of primitive and specialized characters makes the 
Urticales a generalized group. 
