1907] HOLM— VEGETATIVE ORGANS OF RHEXIA 



29 



surface but straight on the ventral; the outer cell wall is moderately 

 thickened, and the lumen of the cells is much wider on the upper 

 ) than on the lower face. Hairs like those described above are fre- 



quent, but the clavate ones occur only on the dorsal face, where 

 the stomata also occur. These are level with the epidermis and are 

 surrounded mostly by four cells of the same structure as the other 

 epidermal cells, that is, the lateral walls are prominently undulate. 

 There is a typical palisade tissue of one layer, and beneath this a 

 pneumatic tissue of about four strata with very wide intercellular 

 spaces. Viewed en face the cells of the pneumatic tissue are star- 

 shaped, interspersed with roundish cells containing druids of calcium- 



oxalate. 



very 



portion of the blade, where the very broad midrib is located. The 

 cuticle is here wrinkled oq both faces, and the lumen of the epidermal 

 cells is narrow, A large colorless parenchyma forms a broad keel 



underneath the midrib, and is thin-walled except where it borders 

 the epidermis. No true collenchyma, however, is developed in any 

 part of the blade, and no stereome. The midrib has no parenchyma 

 sheath and contains one broad, arch-shaped, bicollateral mestome 

 strand and a small supernumerar}^ (fig. 15). This small mestome 

 strand shows the leptome above the hadrome, and is separated from 

 the midrib by a few strands of colorless tissue. 



The very prominent lateral ribs show the same structure as the 

 median, being bicollateral and covered by a colorless tissue on both 

 dorsal and ventral face. 



Rhexia mariana L. 



All the specimens examined proved to be root-shoots. Some of 

 them were quite young and vegetative, but I was unable to detect 

 seedlings.^ This species differs markedly from R. virginica in possess- 

 ing no tuberous roots. The roots that produce the shoots are horizon- 



verv 



observed 



1 

 k 



thinner, lighter brown in color, and branch freely. The shoots in 



The 



figured 



(1:545), but no mention is made of the further growth or as to the occurrence of 



root 



