308 



THE PLANT COVERING OF OCRACOKE ISLAND. 



Mestoine bundles Avith a strong groui) of stereome on\y outside ihe 

 hadrome in young leaves, in older leaves a corresponding grouj) of 

 more numerous and smaller cells outside the leptome also. 



IVA FRUTESCENS L.^ 



Leaf thick, usuall}^ almost vertical, nearly isolateral. 

 Epidermis cells small, walls not undulate, thick, especially the 



outer; cuticle wrinkled, especially above 

 and below the veins; stomata small, about 

 equally numerous on both surfaces, the 

 guard cells sunken, especially on the dor- 

 sal surface, lying irregularly in all direc- 

 tions; hairs on both surfaces (fig. 48) ap- 

 pressed, antrorse, thick-walled, 2 or 3 

 celled, sharp-pointed, the terminal cell 

 abruptly narrowed just above its base, 

 each hair borne upon 5 or 6 radially 

 arranged foot cells which form a cushion 

 that projects above the level of the epider- 

 mis; glands, 2 or 3 celled, sessile, nearly 

 spherical, almost filling depressions in the 

 epidermis and rising slightly above its gen- 

 eral level. 



Hypoderriial collenchyma in strong 

 groups above and below the larger veins 

 (about 10 layers above and below the mid vein). 



Chlorenchyma palisadic, in several layers, the cells small and 

 narrow, those near the mid vein converging toward it; palisade fre- 

 quently interrupted (especiall}^ opposite the mestome bundles) by a 

 few rows of thin- walled, colorless parenchyma (water tissue), which 

 ultimately breaks down into lacunes. Large ducts, each surrounded 

 by a sheath of small cells, occur in the water tissue, esijeciall}^ on the 

 ventral side of the leaf. 



Mestome bundles with a little thin-walled stereome over the 

 hadrome.^ 



Fig, 48.— Ira frutescens— hair from 

 ventral leaf surface. Scale 320. 



^ The material examined was collected near Virginia Beach, Virginia. 



- Iva imbrlcata Walt, is a common plant of the Atlantic sand strand in the 

 Southeastern States, although not observed upon Ocracoke Island. It presents 

 some interesting differences from the salt-marsh /. frufescens. The leaves exam- 

 ined were collected near Cape Henry, Virginia. 



The plant is strongly arom itlc, the leaf perfectly isolateral, fleshy and smooth. 



Epidennis: cells much larger: cuticle not wrinkled; s omata with guard cells 

 level with the ventral surface, somewhat sunken on the dorsal; hairs none. 



Collenchuma less strongly developed than in /. frutescens. 



Chlorenchyma consisting of 2 or 3 layers of palisade on both surfaces. 



Colorless parenchyma (water-storage tissue), filling the interior of the leaf and 

 interrupting the palisade above and below all the veins. 



Mestoine bundles lying in the midst of the water-storage tissue; stereome none. 



The most important differences in /. inibricata are the strong development of 



