29.] 



CHAPTER II. TIJE TISSUES. 



139 



with the naked eye as transparent dots. The development of these 

 oil-glands begins with the division of one or two cells of the 

 young leaf, a group of cells being formed in the cytoplasm of 

 which oil-drops make their appearance. The walls between the 

 cells (Fig. 101 B C) undergo absorption, so that a cavity is formed 

 which is bounded by the closely-packed adjacent cells, and contains 

 a large oil-drop formed by the fusion of the oil-drops of the original 

 cells. 



The most striking examples of schizogenous hollow glands are the 

 various kinds of ducts, such as the resin-ducts which permeate the 

 tissues of most Conif eroe and Anacardiaceae ; the gum- or mucilage- 



FIG. 100 (highly magnified ; after Gardiner). Left-hand figure : transverse section of the 

 margin of a leaf of Saxifraga crustata, showing the chalk-gland e, which is continuous at its 

 base with a vascular bundle ; w water-stoma ; b hairs to which the deposit of calcium 

 carbonate adheres on the evaporation of the exuded drops of water. Right-hand figure: 

 some of the cells of the gland. 



ducts of the Marattiaceae, some species of Lycopodium, Cycads, 

 Canna, Opuntia, etc. ; the gum-resin-ducts of the Umbelliferae, and 

 of some Araliaceae and Composite (Tubuliflorae). Here the cells of 

 the group formed by a series of divisions (Fig. 102 A E), separate 

 from each other so as to leave a passage, of which they form the 

 wall, and into which they pour their secreta. 



(c) Sacs, each consisting of a single cell. To this category 

 belong the cells which contain crystals, as those in the tissues of 

 many Monocotyledons (Fig. 72), in the bast of many dicotyledonous 

 trees, in leaves (Fig. 103) and petioles (Fig. 71) : the cells which 



