Morphological and Anatomical Studies of the Vegetative Organs of Rhexia

Abstract

Considered from an anatomical point of view, these two species may be distinguished from each other by the following contrasting characters: R. virginica.-Roots tuberous where the shoots develop; no stereids outside the leptome of the root; stem broadly four-winged, with three mestome strands in each wing; one central mestome strand in the pith; no cuticular striations above ventral epidermis of leaf; stomata only on dorsal face; midrib with a supernumerary mestome strand; clavate glandular hairs on dorsal face of leaf. R. mariana.-Roots slender throughout; stereids outside the leptome of the root; stem narrowly four-winged, with one mestome strand in each wing; no central mestome strand in the pith; cuticular striations very distinct above ventral epidermis of leaf; stomata on both faces of leaf; midrib without a supernumerary mestome strand; clavate glandular hairs on both faces of leaf. Common to both species are the bicollateral mestome bundles of stem and leaf; the absence of specialized subsidiary cells around the stomata; the absence of mechanical tissues (stereome and collenchyma); the occurrence of two types of glandular hairs; the bifacial structure of the leaves; and the ability of the roots to produce shoots. Vegetative propagation, therefore, depends upon the development of root-shoots, and, upon examining herbarium material, the same mode of propagation was found in R. lutea Walt., in which the roots are very long and slender, and the base of the shoot may persist for more than one season, R. lanceolata Walt., R. serrulata Nutt., and R. ciliosa Michx. All agree with R. mariana in the roots being slender and able to produce shoots. In R. serrulata one specimen appeared as if it was a seedling and blooming in the first season; and one specimen of R. floridana Nash had a tuberous root in addition to the slender, shoot-bearing root. I believe that Rhexia must be placed with that type of plants in which the production of root-shoots is necessary to the normal development of the individual. It is a type poor in representatives, and Wittrock enumerates species of Cirsium, Linaria, Convolvulus, Thesium, Coronilla, Epilobium, and Euphorbia as representing it. Thladiantha dubia Bge. doubtless belongs to this same category, according to Sachs, who states that "the yearly regeneration is dependent upon root-shoots which develop from tuberous swellings of the very long and slender roots." The internal structure of the roots of this curcurbitaceous plant is described by Scott and Brebner, but is very different from that observed in Rhexia.