on the green parts of Hibiscus vitifolius Linn. i95 



Microscopical characters of the outgrowths. 



(a) On the Leaves. The outgrowths on the leaves are of two 

 types, one purely epidermal, and therefore colourless, the other 

 consisting partly of epidermal and partly of sub-epidermal cells. 



An outgrowth of the first type, of median size, mounted as a 

 solid object, is represented in fig. 5. It consists, in this case, 

 of two tiers of elongated cells whose walls, considering the fact 

 that the outgrowths are part of the epidermis, are rather thin. 

 The cells are usually twisted round one another spirally, especially 

 in those outgrowths which are longer than the one represented. The 

 most remarkable point in the structure is the presence of an 

 apical stoma beneath which there is usually no cavity. These 

 smaller and exclusively epidermal outgrowths are colourless, but 

 the larger ones which contain a prolongation of the underlying 

 mesophyll are green at the base. The structure of the outgrowths 

 is rendered clear by a comparison of transverse and longitudinal 

 sections. 



A transverse section of the leaf (figs. 4, 6 and 7) is bounded by 

 an upper epidermis of large cells with a few stomata between 

 them (figs. 4, 6 and 7) and a lower epidermis consisting of smaller 

 cells with more numerous and smaller stomata (figs. 4 and 6). 

 On both sides the cuticle is thin. The palisade tissue consists of 

 a single row of elongated cells, and the spongy parenchyma is 

 made up of about three rows of irregular cells. Scattered in the 

 mesophyll are large isolated cells containing mucilage. Certain of 

 the epidermal cells also increase in size and become mucilaginous. 

 In addition to these cells mucilage occurs in lysigenous spaces 

 which lie chiefly near the vascular tissue in the leaf, and also in 

 the pith and cortex of the stem. Cells containing crystals of calcium 

 oxalate are generally numerous, both in the leaves and in the 

 stem, but bear no definite relation to the outgrowths (figs. 14, 15 

 and 16). 



Figure 6 shews, in longitudinal section, a small outgrowth 

 consisting only of epidermal cells, which are elongated and in 

 close contact with one another. They contain large nuclei and 

 are lined, rather sparely, with a finely granular protoplasm. The 

 nuclei, perhaps on account of the small quantity of protoplasm, 

 are usually closely pressed against the wall (always the inner wall) 

 and sometimes even appear very elongated. Imbedded in the 

 protoplasm of the cells of the outgrowth, and also of the ordinary 

 epidermal cells are numerous very small leucoplasts. Usually 

 drops of oil, some minute, others as large or larger than the 

 nuclei, are abundant in all the colourless cells 1 (figs. 15 and 16). 



1 These drops stain dark brown with 1 °/ osmic acid, are insoluble in ether 

 and alcohol, and swell with 5°/ potash. Their absence in some of the sections is 

 due to the methods of preparation employed. 



