SUNFLOWER. LEAF. 93 



vascular bundles, are found scattered through the 

 thinner part of the section. 



Next examine the thinner part of the section, or the 

 Lamina proper with a high power, and, starting the 

 study of the several tissues from the upper surface. 

 Note successively the following tissues : 



1. Upper layer of Epidermis, continuous with 

 that covering the nerve ; it is a single layer of cells, 

 covered externally by Cuticle, and with the same 

 characters as that of the stem (cf. p. 51). It bears 

 numerous multicellular hairs (already studied in con- 

 nection with the apical bud). Stomata occur in 

 considerable numbers (cf. infra). Beneath this layer 

 lie- 



2. Thin- walled, oblong cells, with copious protoplasm, 

 and chlorophyll grains ; they are arranged with the 

 longer axis perpendicular to the outer surface, and 

 form two layers; this tissue, from the form and 

 arrangement of the cells, is called the Palisade 

 parenchyma ; below it is 



3. A mass of parenchymatous cells of irregular form, 

 with large intercellular spaces ; in general characters 

 they resemble (2) ; this is the Spongy parenchyma. 



(2) and (3) are together included under the general 

 term Mesophyll. Embedded between (2) and 

 (3) are 



4. Numerous smaller vascular bundles (nerves) 

 of various size, often reduced to a single pitted or spiral 

 tracheide, surrounded by a colourless sheath of paren- 

 chyma similar to those in the petiole. The course of 

 these bundles is diverse, since they form the reticulate 

 system of veins ; they may thus be seen in the sections 



