MORPHOLOGY OF HIGHER PLANTS. 211 



face, and if they are much reticulated in addition, the surface is 

 described as reticulate. 



The epidermis is further characterized by the presence of 

 stomata and water-pores, the origin and function of which have 

 already been described (p. 193). 



The parenchyma of leaves, known as mesophyll, may be of 

 two kinds: one in which the cells are nearly isodiametric, or 

 branching, and between which are large intercellular spaces ; and 

 another, consisting of elongated cells, which are compactly ar- 

 ranged, and known as the palisade cells. The latter usually 

 occur beneath the upper epidermis, as in coca (Fig. 261), digi- 

 talis and pilocarpus (Fig. 257) ; or they may occur upon the 

 lower surface as well, as in senna (Fig. 263) ; or they may con- 

 stitute the entire parenchyma of the leaf, as in eucalyptus. Oil- 

 secretion reservoirs are sometimes found in the parenchyma, as 

 in pilocarpus (Fig. 257) and eucalyptus, when the leaf is said to 

 be glandular-punctate. 



The fibrovascular tissue of the leaf consists of xylem and 

 phloem, surrounding which is a layer of cells corresponding to 

 the endodermis or bundle-sheath of the young stem. This tissue 

 is found in the middle of the veins, the phloem being situated on 

 the side toward the upper surface of the leaf, and the xylem to- 

 ward the under surface. Collenchyma is frequently found under 

 the epidermis of the veins of the leaves, as in Mentha piperita, 

 seiina (Fig. 263) and stramonium (Fig. 117). 



INNER MORPHOLOGY OF THE FLOWER. 



The inner structure of the flower bears a close resemblance 

 to that of the stem and leaf. The bracts in almost all particulars 

 are like the foliage leaf of the same plant and the flower stalk 

 closely resembles the foliage stem. The calyx, while resembling 

 the foliage leaf, usually contains calcium oxalate in greater 

 amount, and the mesophyll consists wholly of rather loose chloro- 

 phyll parenchyma; the outer or under epidermis contains the 

 stomata, and if hairs are present, they also arise from this surface ; 

 the fibrovascular bundles are generally simple in structure, al- 

 though in some cases, as in lavender, sclerenchymatous fibers are 

 strongly developed. 



