32 BOTANICAL GAZETTE [july 



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 wdthout a supernumerary mestome strand; 

 clavate glandular hairs on both faces of leaf- 



Common to both species are the bicoUateral mestome bundles 

 of stem and leaf; the absence of specialized subsidiary cells around 

 the stomata; the absence of mechanical tissues (stercome and coUen- 

 chyma); 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 pro- 

 duce 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 devel- 

 opment 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 obser\Td in Rhexia. 



Brookland, D. C. 



7 Vorlesungen iiber Pflanzen-Physiologie 28. Leipzig. 1882. 



8 Annals of Botany 5:273. 189c. 



i 



