CHLOROPLASTS AND CHLOROPHYLL 



105 



FIG. 115. Upper epidermis and palisade cells of 

 a buttercup leaf 



A, section perpendicular to upper surface; B, exte- 

 rior view of upper surface with palisade cells seen 

 through epidermis ; e, epidermis ; p, palisade cells. 

 Much magnified. After Bonnier and Sab Ion 



walnut leaf about 



300,000 per square 



inch of the lower 



epidermis. 



124. The meso- 



phyll ; chloroplasts ; 



chlorophyll. The 



mesophyll appears to 



the naked eye 'of a 



uniform green, but 



under the microscope 



its cells are seen to 



contain many green 



structures called chlorophyll bodies or chloroplasts (" chlorophyll" 



meaning leaf green and " chloroplast " meaning molded out of 



green material). The color of the leaf, as well as that of green 



stems and other parts of the plant body, is due to these. A 

 chloroplast is usually, in seed plants and 

 in the higher spore plants, of an ellipsoidal 

 form or lens-shaped 

 and somewhat 

 translucent. Its 

 color is due to a 

 green substance, 

 soluble in alcohol 

 but not in water, 

 known as chloro- 

 phyll. 



125. Woody tis- 

 sue in leaves. The 

 veins of leaves con- 

 sist of nbro-vascular bundles containing 



wood libers and vessels much like those 



of the stem of the plant. Indeed, these 



bundles in the leaf are continuous with 



FIG. 116. Passage of a 

 fibro-vascular bundle 

 from stem to leaf of 

 a buttercup (diagram- 

 matic) 



s, stem ; w, woody part of 

 bundle; b, sieve cells of 

 bundle. After Bonnier 

 and Sablon 



FIG. 117. Diagram of 

 distribution of fibro- 

 vascular bundles in the 

 leafstalk of a buttercup 



epidermis ; w, woody 

 part of bundle; b, sieve 

 cells of bundle ; /, fibrous 

 layer on outer part of 

 bundle. Magnified. 

 After Bonnier and Sa- 

 blon 



