ANATOMY OF BACCIIARIS HALIMIFOLIA. 307 



Colorless parenchyma (water-storage tissue) above and on each side 

 of the midvein. 



Mestome bundles without stereome supports, but with a small irreg- 

 ular group of collenehyma lying outside the hadrome, 1 



BACCHARIS HALIMIFOLIA L. 



Leaves thiekish, nearly vertical, isolateral. 



Epidermis: Cell walls not undulate, thickened, the outer ones greatly 

 so; cuticle warty, especially on the dorsal surface; stomata mostly 

 parallel to the veins, but many somewhat deflected, guard cells slightly 

 prominent, each stoma radially bordered by 4 or 5 small epidermis 

 cells. 



Collenehyma (hypodermal) replacing chlorenchyma above and below 

 the larger veins (0 or 7 layers below the leptome of the midvein), 

 containing no ducts. 2 



Chlorenchyma: Palisade occupying the whole thickness, of the leaf 

 between the veins, rather open, especially that in the interior of the leaf 

 (but typical pneumatic tissue none), converging toward the midvein 

 on the dorsal side; large, deep air chambers underneath the stomata. 



Colorless parenchyma (water tissue) in 2 layers on each side of the 

 midvein (cells circular in cross section), in a single layer entirely sur- 

 rounding the smaller bundles. 



1 Three nonmaritime species of Aster were selected for comparison with the two 

 salt-marsh species: A. puniceus, a broad-leaved plant of boggy ground, and J.. 

 dumosus and A. erieoides, narrow-leaved species of dry, sandy soil. 



A. erieoides has a practically isolateral leaf, epidermis alike on both faces, with 

 undulate radial and thickened outer walls, finely wrinkled cuticle, guard cells of 

 the stomata level with the ventral surface, slightly prominent on the dorsal sur- 

 face; chlorenchyma near both surfaces compact and small-celled, more open and 

 larger-celled in the interior of the leaf; hypodermal collenehyma in 2 layers above 

 and below the midvein; water parenchyma none. 



A. (iumoitus has a distinctly bifacial leaf, epidermis much as in .1. erieoides, but 

 the 3 surfaces more differentiated, the ventral with radial cell walls less undulate 

 and outer walls less thickened than in A. erieoides, cells larger and stomata much 

 fewer on the ventral surface, the dorsal with radial walls more strongly undu- 

 late, and scattered, slender, pointed, few-celled hairs along the veins: palisade com- 

 pact, pneumatic tissue open: veins supported by hypodermal collenchymatic tissue. 



A. puniceus shows, of course, the greatest amount of difference from the salt- 

 marsh forms. It has a flat, approximately horizontal, bifacial leaf. The ventral 

 surface is rough with thick- walled, prickle like, 1 -celled hairs, mixed with scat- 

 tered, longer, more slender, and thinner-walled hairs; the stomata lie in all direc- 

 tions in and have their guard cells level with the dorsal surface, but are wanting 

 on the ventral face; the cuticle is smooth; the chlorenchyma is differentiated into 

 a single layer of compact palisade and a few layers of rather open pneumatic tis- 

 sue; no colorless parenchyma occurs inside the epidermis. 



On the whole the salt-marsh Asters show less anatomical divergence from inland 

 forms than does the salt-marsh Solidago. Of the two species, A. tenuifolius 

 exhibits a more distinctive halophytic, or rather xerophytic, structure than does 

 A. subulatus. 



"Warming, Halofyt-Studier, p. 195, describes ducts which occur in the collen- 

 ehyma of the leaf of Baccharis dioica. 



