1912] STARR— ANATOMY OF DUNE PLANTS 299 



in true dune plants and generally admitted to be xerophytic. 

 Stomata appear only on the under sides of leaves of both forms 

 except in the cases noted, where they appear on both sides; there 



which 



stomata on the upper surface also. 



me 



from 

 In 



humus 



changing the water content and other soil relations, and xerophytic 



made enough shade and urotection for mes 



come 



in, so woods have developed. The exposure must 



be less here and the water relations better than on dunes with 



scantier vegetation, yet leaves of Fraxinus, Cornus, and Ostrya 



collected in these woods were thicker than some of the dune forms. 



The internal structure of Fraxinus differed from the dune form, 



the palisade consisting of a single layer of cells, not compactly 

 arranged. 



Another interesting variation comes out in the comparison of 

 leaves of different seasons. Those collected in 191 1 are frequently 

 thicker than those collected in 1909 in the same habitat, so that 

 the mesophytic form of 191 1 is sometimes thicker than the xero- 

 phytic form of 1909, but the xerophytic form of 191 1 is correspond- 



increased. The season was an unusual one, showing 

 temperatures of 39 , 46 , and 66°, for March, April, and May, in 

 which time the leaves became fully mature, the normal being 

 34-4 , 45-9°j and 56.5°. In 1909 the tempera tui 



in 



the normal 



sunshine ai 

 March and May 



considerably above the average, though April went below. Precipi- 

 tation was near the normal except in March, when it was only a 

 little more than half. Winds were not unusually high. The 



must have been due, at least in 



high 



three months, sunshine 



March. 



March and May 



The accompanying table (II) gives a comparison of mesophytic 

 and dune forms as to nine characters of the stem. 



