276 BOTANICAL GAZETTE [October 



the study of the conducting and mechanical tissues of the leaf, a 

 section of the midrib was taken at the base of the blade. For the 

 study of the stems, sections 5 mm. in diameter were used; when 

 this was not possible, the two compared were as nearly equal as 

 obtainable. Cannon's method of counting was adopted. A circle 

 14 cm. in diameter was drawn on paper and octants were marked 

 off. With a camera lucida an image of the section was so thrown 

 on the paper that the arc of the octant coincided as nearly as pos- 

 sible with the periphery of the wood cylinder. The area of the 

 octant was 18.24 sq. cm. (i4 2 Xo.7845-f-8). Since the magnifica- 

 tion used was 100, the area examined was o. 19 sq. cm. or 19 sq. mm. 

 For the size of the vessels and fibers measurements were always 

 made in the last spring wood, or if that was not fully organized, in 

 the preceding. In the following tables M stands for the mesophytic 

 form and X for the dune form ; T for the average thickness of leaf, 

 with minimum and maximum in parenthesis; UE for thickness of 

 the upper epidermis, including cuticle; P for depth of palisade; 

 Sp for depth of sponge; LE for thickness of lower epidermis; OW 

 for outer wall of the epidermis (including cuticle); and Cu for 

 cuticle. The percentages are of the entire thickness of the leaf. In 

 the table of stems N stands for the number of vessels in the octant; 

 D for the average diameter of the larger vessels, with the maximum 

 in parenthesis; W, the thickness of the walls of the vessels; F, the 

 thickness of the walls of the fibers; L, the lumen of the 'fibers; R } 

 the number of growth rings; C, the thickness of cork; and 5, the 

 thickness of the sclerenchyma ring or of the isolated masses of 

 sclerenchyma that often appear in the cortex. As the size of 

 vessels, being tubes, varies as their cross-sections and as the cross- 

 sections vary as the squares of their radii, it is evident that the ves- 

 sels in an octant of a mesophytic form would compare with the 

 vessels in an octant of the corresponding dune form as the products 

 of the number of vessels by the squares of their radii. Where the 

 result is not evident at a glance, the radius was squared and the 

 product found. The measurements are all in microns, though the H> 

 is omitted after the first, as is also the per cent sign. 



