LESSON 16.] LEAVES. 47 



278. It is formed of two distinct series of cells, each containing 

 chlorophylle, or green colored granules, but differing in their form 

 and arrangement. This is best seen by making a vertical section of 

 a leaf and examining it by the microscope. One of these layers is 

 connected with the upper surface, and consists of compact oblong 

 cells placed endwise (Fig. 82, a) ; the other, connected with the lower 

 side, consists of loosely aggregated cells, having numerous cavities 

 between them (5), and, when these cells have an elongated form, 

 their long diameter is always parallel with the cuticle. 



279. The cells on the upper side are usually placed close to each 

 other, without any space between them, except in cases where sto- 

 mata occur (e). 



280. The figure (82) represents a section of a melon leaf, per- 

 pendicular to the surface. The upper cuticle is marked c; it shows 

 hairs (d) on its surface, and two openings of stomata (e). Below the 

 upper cuticle are layers of oblong cells (a), with two spaces between 

 them (/), communicating with stomata. The lower cuticle (g) } also 

 exhibits hairs and stomata; and above it are layers of loose cells (5), 

 with numerous lacimse (openings, h). The vascular bundles running 

 through the parenchyma are marked i. 



281. In a vertical section of a leaf of the common garden Balsam 

 (Balsamina hortensis. Fig. 83), we see 



the upper cuticle at a ; in the section 

 from which the drawing was made, al- 

 though only one layer of cells thick, 

 there are two, and three layers of the 

 upper and under cuticle. A double 

 series of compact, oblong cells, beneath 

 the upper cuticle are shown at 6, the 

 smaller cells, belonging to the central, 

 and under portion of the leaf, c ; be- 

 tween this layer are two spiral vessels, 

 d; the under cuticle, containing nu- 

 merous stomata, e. 



282. The green color of leaves is 

 wholly due to the chlorophylle (chloros, 

 green; phyUum, a leaf) contained in 



the oblong and other shaped cells; in this respect these cells bear 

 very close analogy to the color-producing or pigment (paint] cells 

 of the human family, and other animals. 



283. The dark color of the skin of a negro, or of an Indian, is 



