304 



THE PLANT COVERING OF OCRACOKE ISLAND. 



Hypoderm continuous, 1-Ui3'ered. Outer cortex with rather thick- 

 walled cells, containing chlorophyll; inner cortex gradually becoming 

 thinner- walled and colorless. 



Stereome in a concentric band of isolated groups, lying Inside the 

 middle of the cortex. 



Lactiferous ducts few, Ijang just outside the mestome bundles. 



Mestows hundles bicoUateral, 

 perileptomatic, the leptome most 

 strongly developed on the outer 

 l^eriphery of the hadrome. 



LiPPIA NODIFLORA Mx. 



Leaf^ imperfectly bifacial, usu- 

 ally horizontal, but sometimes 

 vertical. 



Epidermis alike on both sur- 

 faces, cell walls thick, not undu- 

 late; cuticle wrinkled; stomata 

 (fig. 47) lying in all directions, 

 guard cells almost level with the 

 ventral surface, slightly depressed 

 on the dorsal surface, each stoma 

 bordered by 2 crescent-shaped, 

 chlorophyll - holding, subsidiary 

 cells which are usually at right 

 angles to but often nearly or quite 

 parallel to the guard cells, and of 

 which one is usuallj^ considerably 

 larger than the other; hairs abun- 

 dant on both faces, iDarallel to the 

 veins, appressed, lying in slight 

 grooves of the epidermis, each attached b}^ its middle (hence 2-armed) 

 to a short cylindrical foot cell, which is bordered by several wedge- 

 shaped (as seen from above) radiallj^ arranged epidermis cells, the 

 free cell with a very thick, warty cuticle. 



Hypodermal collenchynla (not very typical), in 1 or 2 layers above 

 and 3 or 4 below the principal veins, intermitting the chlorenchyma 

 in full-grown leaves. 



Chlorencliyma: Palisade 2-layered, the cells rather short; pneu- 

 matic tissue rather compact, not well differentiated from the palisade, 

 but its cells more nearly isodiametric and containing less chlorophyll. 

 Mestome hundles (of larger veins), with some stereome below the 

 leptome and a small group of collenchj^ma above the hadrome, which 

 finall}^ becomes continuous with the subepidermal group of col- 

 lenchj^ma. 



Fig. 47.—Li2ypia nodiflora— stomata and hairs, 

 a, Stomata on leaf; t», hair and stoma on ventral 

 leaf surface; c, hair on dorsal surface. Scale 

 240. 



' Compare Warming. Halofyt-Studier, p. 3oo, and Solereder, Syst. Anat.,p. 713, 



