178 PRACTICAL BOTANY 



haematoxylin, and mounted in Canada balsam, stages of division 

 of the nucleus may be observed in the cells which are about to 

 divide into the two guard-cells. 



It is more difficult to trace the development of the stoma of 

 the Maize ; but it may be done in the same way in a foliage-bud. 

 The main point of difference is that after the mother-cell of the 

 etoma has divided to form the two guard-cells, two other cells are 

 cut off from the neighbouring epidermal cells (subsidiary cells) : 

 these lie parallel to the guard-cells. 



Further, the epidermis of the Maize is complicated by short 

 cells, which appear in irregular groups among the ordinary 

 epidermal cells : .this is a common character among the 

 Grasses. 



VIII. Sections should also be made through the 

 fleshy scales of the bulb, and these will show the same 

 general arrangement of tissues as the foliage-leaves, 

 but the colourless parenchyma is much more bulky, 

 and is densely stored with starch : numerous cells con- 

 taining raphides will be found, especially towards the 

 outer (lower) surface of the scales. 



Note on crystals. 



Cut longitudinal sections of the scape or leaves of the 

 Hyacinth or Onion : many other Monocotyledons will do as well : 

 mount in water, and observe the large cells containing numerous 

 needle-shaped crystals (Raphides) arranged in a bundle parallel 

 to one another. In order to investigate their nature the follow- 

 ing tests may be applied : 



a. The attempt may be made to stain them with iodine, or 

 other' stains which colour crystalloids, but they will not be 

 affected : they are thus distinguished at once from crystalloids. 



b. Irrigate a section with acetic acid : they are not affected : 

 they are therefore not calcium carbonate. 



c. Irrigate with dilute nitric acid : the crystals are dissolved. 



d. Irrigate a fresh preparation with a small quantity of dilute 

 sulphuric acid : the crystals will be dissolved, and crystals of a 



