274 



Atriplex vesicarium. (Figs. 17 and 18.) 



The leaves of Atriplex vesicarium vary rather widely in shape from elliptical 

 or oblong lanceolate to obovate and with entire or deeply indented margins. The 

 epidermis consists of fairly small cells not cutinised, but with cellulose walls 

 which are somewhat thicker than those of the mesophyll cells. All the epidermal 

 cells have living contents. The stomates are simple guard cells placed on the 

 same level as the epidermal cells and not protected by any projecting ridges. 

 Underneath the epidermis on both sides of the leaf is a layer of rather large cells 

 packed loosely together and containing no chloroplasts, but with clear watery 

 contents and also many crystals of calcium oxalate. This is termed the hypo- 

 dermal layer (fig. 17). 



The midrib is composed of two vascular bundles, non-lignified fibres being 

 scattered between both the xylem and phloem elements. CoUenchyma is developed 

 above and below the midrib. The margins of the younger leaves also have a 

 strengthening collenchymatous tissue. Monteil (1906) describes A. vesicarium 

 as having five vascular bundles in its midrib. The writer has examined leaves 

 from several different plants of A. vesicarium, and in no case has he found this 

 to be the case. It is doubtful whether Monteil was dealing with A. vesicarium, 

 since he regards the leaf type as being near to that of A. rosea. In this' species 

 the mesophyll is not arranged radially around the nerve sheath, no hairs are 

 developed, and no chlorenchymatous sheath is present around the midrib. 



The midrib and secondary veins are surrounded throughout their whole 

 length by a sheath of thick walled, practically cubical cells containing chlorplasts 

 and very numerous starch grains. Surrounding these cells lies an outer sheath 

 of thin walled palisade cells. They contain relatively little starch, from which 

 it appears that the thicker walled cells around the veins have a collecting or 

 storage function. 



The epidermis on both dorsal and ventral sides is thickly covered with large 

 bladder-like hairs. The cells have cellulose walls and a very thin lining of living 

 protoplasm. In the older leaves these hairs are compressed to form a network 

 as shown in fig. 17, the individual cells arising, to all appearances, from several 

 epidermal cells and interlocking fairly tightly with few intercellar spaces. To 

 determine the origin of these hairs a young leaf was taken from a bud and 

 examined in transverse section. Hairs were found in all stages of development ; 

 they arise from a single basal epidermal cell, have a stalk cell and a single 

 large terminal cell. All three cells at this stage have quite dense protoplasmic 

 contents (fig. 18a). The stalk cell elongates (fig. I8b) and the bladder assumes 

 considerable proportions. Later, it appears that the stalk cell degenerates and 

 many of the large terminal cells become joined together by the union of their 

 cellulose walls. These large cells are considered to function as water-storing 

 vesicles. 



In conclusion, it may be remarked that A. vesicarium bears a striking 

 resemblance to A. Halimus, described by Volkens (1887) from the Arabian 

 desert — an example of the similar structural modifications produced under 

 similar conditions. 



Rhagodia Gaudichaudiana. (Fig. 19.) 



This plant is a weak shrub and usually straggles over other bushes. The 

 leaves are hastate and their structure is comparatively simple. The mesophyll 

 throughout consists of rather spherical cells containing plastids. There is no 

 differentiation into palisade and spongy parenchyma. Large water-storing cells 

 with clear contents are found irregularly scattered through the mesophyll tissue. 

 These large cells usually contain crystals of calcium oxalate. The midrib and 

 secondary veins are simple vascular strands. There is a little collenchyma 

 developed underneath the midrib, otherwise mechanical tissue is lacking. The 



