ANATOMY OF MONNIERA AND SOLIDAGO. 305 



MONNIERA MONNIERA (L.) BRITTON. 1 



Occurs in 2 forms; one in shallow pools, largely submersed, with 

 long stems, elongated internodes, and larger leaves; the other terres- 

 trial, in wet sand, with short, creeping stems, contracted internodes 

 and smaller leaves. 



(a) Aquatic form. Structure thai of a parlially submersed hydro- 

 phyte, with thin-walled tissues, much reduced mestome system, no 

 mechanical tissue, etc. 



Leaf isolateral. 



Epidermis: Cells with undulate lateral walls, the walls thin except 

 the outer, which is somewhat thickened; cuticle delicately wrinkled; 

 stomata more numerous on the dorsal surface, guard cells about level 

 with the epidermis, bordered by 2 to 1 ordinary epidermal cells; hairs 

 none. 



Chlorenchyma homogeneous, palisade none. 



Mestome bundles immediately bordered by chlorenchyma, not rein- 

 forced by stereome or collenchyma. 



Stem: Epidermis as in the leaf. 



Cortical parenchyma in 1 or 2 continuous layers just beneath the 

 epidermis and around the central cylinder, elsewhere in 1-layered 

 plates, separating the large lacunes. 



Mestome cylinder composed of several bundles, inclosing a small 

 quantity of pith. 



(b) Terrestrial form. The only tangible differences from the aquatic 

 form are: Stomata about equally numerous on both leaf surfaces; 

 mestome bundles somewhat more developed and walls of the vessels 

 more lignified; mesophyll somewhat more compact. 



Solid ago sempervirens L. 2 



Leaf somewhat fleshy, vertical or nearly so, approximately isolat- 

 eral. 



Epidermis: Cells with nonundulate radial walls, only the outer 

 strongly thickened, except above and below the larger veins; cuticle 

 strongly wrinkled; stomata numerous on both faces with guard cells 

 level with the surface, bordered by usually i ordinary epidermal cells; 

 hairs none. 



Hypodermal collenchyma in only 1 or 2 narrow layers above and 

 3 or 4 wide layers below the larger veins. 



Chlorenchyma homogeneous, none of it typical palisade, frequently 

 interrupted, especially opposite the mestome bundles, by plates of 

 colorless, thin- walled parenchyma (water tissue), which extend from 

 the ventral to the dorsal epidermis, and ultimately break down into 

 large lacunes close; beneath the epidermis. 



1 Herpestis monniera H. B. K. 



3 The material examined was collected at Virginia Beach, Va. 



2965 ± 



