1907] HOLM— VEGETATIVE ORGANS OF RHEXIA 31 



I 



The stem ' 



The basal intemodes are cylindric; those above are obtusely 

 quadrangular, with four very narrow wings; hairs like those described 

 under the foregoing species cover the stem. The cuticle is very 

 prominently wrinkled, and the epidermis is thin-walled. The cortex 

 is broken down in wide lacunes in the basal internode, but solid in 

 the upper internodes. No collenchyma or stereome was found in 

 the stem. There is only one small collateral mestome strand in each 

 of the four wings, and sometimes one or two between them. The 



stele represents two arches within the slightly convex faces of the 

 stem, and consists of bicollateral mestome strands with much leptome 

 on the inner face of the hadrome. The pith is thin- walled and does 

 not contain any isolated central strand of leptome; neither druids 

 nor starch were observed. Pericyclic cork is developed, but only 

 in the basal intemodes. 



J 



The leaf 



The cuticular striations over the ventral epidermis (figs. 8 and/^), 

 which radiate toward the center of the outer cell wall, are characteris- 

 tic of the leaf structure. The lumen of the epidermis is considerably 

 wider on the ventral surface than on the dorsal, and the stomata 

 . {fig- 7) are not confined to the latter. They show the same structure 

 as those of the other species, and some were noticed on the ventral 

 face of the leaf-blade. Hairs of both kinds described above are 



w 



scattered over both faces, and also along the margins. The chloren- 

 chyma shows the same structure as observ-ed in R. virginica, but the 

 pneumatic tissue is less open. The midrib lacks the supernumerary 

 ventral mestome strand, but otherwise the structure of the veins is 

 identical with that of the former species. 



* 



Summary- 

 Considered from an anatomical point of view, these two species 

 niay 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, 

 ^ith three mestome strands in each wing; one central mestome strand 

 "1 the pith; no cuticular striations above ventral epidermis of leaf; 



