HISTOLOGY OF ANGIOSPERM STEM, ROOT, ETC. 123 



epidermis of both sides and merges into spongy tissue in which are 

 embedded vascular bundles arranged somewhat irregularly but 

 having the phloem turned towrads the leaf surface to which the 

 bundle is nearest. This structure is also shown by phyllodes 

 (laterally flattened petioles) in various species of Acacia, etc., 

 sections of which should be examined. For the more or less 

 markedly centric type of leaf, which is cylindrical or prismatic 

 and shows little or no distinction of upper and lower surfaces, 

 examine sections of the leaves of Onion, some species of Juncus, 

 Stonecrop, Sea Elite (Suaeda), Prickly Saltwort (Salsola), etc. 



152. Water-stomata. Mount in water pieces cut from the 

 margin of a Tropaeolum leaf, and on the upper side at the margin 

 note the numerous water-pores in groups at the ends of the chief 

 veins. The guard-cells of these pores having usually lost their 

 living contents at an early stage in the development of the leaf, 

 the water-stoma remains wide open it has lost the power of move- 

 ment. These pores can be seen more clearly in tangential sections 

 cut from the margin of the leaf. 



153. Water-Glands (Hydathodes). For the structure of the 

 water-glands which are often associated with water-pores examine 

 a Fuchsia leaf, in which these glands appear as swellings on the 

 edge, each gland being on a tooth at the termination of a vein. 

 Cut off, mount, and examine the tip of a tooth, to see the large 

 water-stoma. 



Cut vertical sections, so as to traverse tooth, vein, and gland 

 longitudinally, and note (1) the epidermis on either side, inter- 

 rupted at the tip of the tooth by (2) the water-stoma ; (3) the 

 widening out of the bundle and its termination in the glandular 

 (epithem) tissue a mass of colourless parenchyma ; (4) the water- 

 cavity at the end of the gland, below the stoma. 



154. Chalk-glands. These are modified water-glands, found 

 in various Saxifrages, etc. Note the white masses on the leaf- 

 margin in one of these plants ; treated with acetic acid, the masses 

 dissolve with effervescence, since they consist of calcium carbonate 

 deposited on the evaporation of the water excreted by the gland. 

 The structure is much the same as in Fuchsia ; note the short hairs 

 on which the lime is deposited. 



155. Structure of Grass Leaf. Cut transverse sec- 

 tions of the plumule of a Wheat seedling, and note (1) the 

 tubular sheath, consisting of colourless parenchyma and 

 containing two opposite vascular bundles ; (2) the young 

 foliage-leaves enclosed in the sheath. 



