1894.J MICROSCOPICAL JOURNAL. 327 



thin pieces crossing a vein and shows the thickening 

 where the vein lies in the center and the thinner blades 

 on each side. A very good way to cut such a "section" 

 as this is to place a small piece of leaf between two 

 pieces of elder-pith and with a sharp scalpel to slice 

 down, cutting as thin as possible. The slices should be 

 floated oflf into a shallow glass of water and then the thin- 

 nest of them floated onto a slide in water and covered 

 for examination. 



Figure 1, which is somewhat diagrammatic, was made 

 from such a section. It shows a number of structures 

 which help us to solve the problem of the leaf. We see 

 a thin skin («) covering the central mass of material, and 

 this we suspect of being the stuff which keeps the water 

 of the leaf from instant evaporation in spite of the fact 

 that it is spread out in so thin a layer and exposed to 

 air on both sides. Then we see, in the center, a mass of 

 denser material (b) which we recognize as the cut end of 

 the vein, and we see that it is but a small portion of the 

 entire amount of leaf material by which it is surrounded. 

 Then, too, on the surface at various places we see minute 

 projecting bodies which we doubtless recognize as the 

 parts causing the velvety surface. They are called "hairs" 

 and are of three forms. The whole general thickness of 

 the leaf is about one one-hundredth of an inch. 



If the section is thin enough, the high power will pre- 

 sent a view somewhat like figure 2, wliich is magnified 

 not far from four hundred diameters. Here two entirely 

 distinct types of cells come to view. On the surface are 

 long and narrow cells {ep), whose outer side is very thick 

 and dense. These are "epidermis." They are not green 

 as are the cells in the interior, but are colorless. They 

 are apparently empty, but if a section be properly treated 

 for shrinking the protoplasm of these cells, a layer 

 closely lining the wall of the cell will be discovered 

 as seen in figure 6 {pr). In the section beneath the 



