76 HARSHBERGER— LEAF STRUCTURE OF [April 23. 



possesses great power of resisting the action of sodium chloride 

 in solutions as strong, as sea water. This is reflected in their 

 structure. 



Structural Adaptations. 



These will be treated as applicable to the strand plants, as one 

 category, and to the salt marsh plants as the other. 



Strand Plants. — The leaf adaptations to light are found in the 

 increased number of palisade layers, their presence on the upper 

 and under sides of the leaves and their arrangement, so that the 

 central part of the leaf becomes palisade throughout. When both 

 leaf surfaces are equally illuminated, the leaf may be termed iso- 

 photic, when unequally illuminated, diphotic. Diphotic leaves which 

 show a division into palisade and spongy parenchyma have been 

 called by Clements diphotophylls. Isophotic leaves are of three 

 types, viz., the staurophyll, or palisade leaf ; the diplophyll, or double 

 leaf; the spongophyll, where the rounded parenchyma cells make 

 up the bulk of the leaf in cross-section. Succulent leaves are those 

 developed for water storage and to some extent the presence of 

 latex provides against desiccation. The depression of the stomata, 

 the development of a thick cuticle, the presence of a hypodermis 

 of thick-walled cells, the presence of hairs and the formation of 

 air-still chambers by a folding of the leaf tissue are all structures 

 which assist in the regulation of transpiration. The following 

 is a classification of the different leaf structures with reference to 

 the strand plants which illustrate such adaptive arrangements. 



Thick Cuticle : Ammophila arenaria, Quercus obtusiloba, 

 Ilex opaca. 



Thick Epidermis : Baccharis halimifolia, Ampelopsis quinque- 

 folia, Euphorbia polygonifolia, Cakile edentula. 



Hypodermis Present: Ammophila arenaria. 



Two or More Rows of Palisade Cells : Lathyrus maritimus, 

 Strophostyles helvola, Ampelopsis quinquefolia, Quercus obtusiloba, 

 Vitis Labrusca, Ilex opaca, Baccharis halimifolia. 



Stomata Depressed (slightly) : Euphorbia polygonifolia, Lathy- 

 rus maritimus, Ilex opaca, Hudsonia tomentosa; (deeply) Am- 

 mophila arenaria, Lathyrus maritimus (Sea Side Park), Atriplex 

 hastata, Vitis Labrusca. 



