The Prevalence of Green Color in Plants 21 



universal cellular structure into his visual conception of plants. 

 In our picture (figure 2), carefully drawn from an actual leaf, and as 

 well in the conventionalized leaf (B on Plate I), the reader can 

 see for himself the cells of the upper and lower skin (or epidermis), 

 those of the vein (the clearer mass lacking chlorophyll), and 

 finally those of the green tissue, distinguished by the large black 

 or green spots which represent the chlorophyll grains. For the 



FIG. 2. A thin slice, or section, cut across a typical leaf (the European Beech), and highly 

 magnified. From a wall-chart by L. Kny. In the original, the numerous black discs 

 are green, as in the living leaf. 



chlorophyll really is contained in definite grains, and is not a dye 

 spread all through the leaf. These cells are roughly spherical, 

 cylindrical, or polygonal in shape, though the open clear air- 

 spaces between them are most irregular in form. Each cell has 

 its outer thin transparent wall (little more than a line in figure 2), 

 within which comes a complete lining of a thin gelatinous sub- 

 stance (shown in Plate I, B, by the faint grayish or dotted 



