272 



Fig. 16. 

 Transverse section through portion 

 of stem of Pholidia scoparia, show- 

 ing sunken stomate and protecting 



scale. 

 s., Scale; g.c, Guard cell. X94. 



Pholidia scoparia. (Figs. 14, 15, and 16.) 



Some of the features of Pholidia scoparia have been described by Cannon 

 (1921) in his general survey of the genus Eremophila. 



Pholidia scoparia is a "switch plant." The leaves are small, and the func- 

 tions of photosynthesis and transpiration are undertaken by the stems also. As 

 mentioned before, the areas of leaves and stem were calculated separately, and 

 it was found that two-thirds of the total area was due to the stem. The stem 

 in transverse section has roughly the form of a short cross (fig. 14). The 

 epidermal cells are larger than those of Geijera parviflora, and also have their 

 outer walls cutinised, though not so heavily. The stomates are simple guard 

 cells sunken below the epidermis (fig. 16). No protecting ridges are developed. 

 The surface of the epidermis is covered with scales whose heads overlap and 

 protect the epidermis generally. Each scale is made up of a disc-shaped head 

 supported on a short stalk attached to a basal epidermal cell. All the cell walls 

 of the scale are thick and cutinised, and appear to have no living contents. The 

 hairs have probably a purely protective function. They are more scattered on 

 the stem than on the leaf. Calcium oxalate crystals are present in many of the 

 epidermal cells. 



The chlorenchyma is composed of rather small, regular, palisade cells and 

 spherical, spongy parenchyma. Oil glands are developed in the mesophyll. These 

 are smaller than in Geijera parviflora. The medulla is formed of large paren- 

 chyma cells containing a good deal of starch. The xylem entirely surrounds 

 the medulla and comprises very small spiral, annular, and pitted vessels. The 

 phloem has fairly large cells. A continuous sheath of phloem fibres surrounds 

 the whole. 



The epidermis and stomates of the leaf are similar to those in the stem, 

 but the scales are more numerous. The leaf (fig. 15) has a central midrib 

 with a little collenchyma developed beneath it. Two smaller veins occur lateral 

 to the midrib. The chlorenchyma is mainly a ring of two rows of palisade cells 

 with a little spongy parenchyma placed centrally. Oil glands are also present 

 in the leaf. 



