WATER-ABSOEPTION AND TRANSPIRATION. 



121 



When the stomates close at night, water is still absorbed 

 by the roots, and in this way a plant which has become wilted 

 on a hot day recovers its turgidity at night. Drops of water 

 may be forced out of the leaves, 

 usually through special openings 

 (water-stomates) at the margin of 

 the leaf. A water- stomate has 

 two guard-cells, but these remain 

 always apart, so that the stomate 

 does not open and close like an 

 ordinary stomate. Water-stomates 

 occur at the ends of the bundles 

 (on the teeth when the leaf -margin 

 is toothed well seen in Fuchsia) 

 and are connected with the bundle- 

 endings by means of a mass of 

 glandular tissue (water-gland). In 

 Saxifrages there are hairs close to 

 the water-stomates, on which lime 

 is deposited as the excreted water 

 evaporates. In G-rasses the water 

 escapes between the ridges of the 

 leaf and, in seedlings at any rate, from the tip of the 

 leaf. 



* (a) Try several plants and find out whether their leaves can absorb 

 water directly. Cut and weigh a leafy twig, or a leafy shoot, or a 

 well-grown seedling ; then plunge it into water, immersing the leaves, 

 for a few minutes ; carefully wipe it dry with blotting-paper or a soft 

 cloth, and weigh again. 



* (6) Cover various growing plants with a bell-jar overnight and look 

 for water-drops excreted by the water-stomates. The plants should be 



f rowing in pots, and the following will usually give good results : 

 uchsia, Tropaeolum, London Pride (a Saxifrage, with chalk -glands). 

 In a cut twig of Cherry, set in water and kept under a bell-jar, drops 

 of water are seen oozing from the glands on the leaf-stalk. 



(c) Cover seedlings of Wheat or Maize with a bell- jar, and note the 

 excretion of water from the tips of the young leaves. 



* (d) Fix a cut piece of a Fuchsia into the short limb of a J -tube, as 

 shown in Fig. 44. Pour some water into the tube and then pour in 

 mercury. Drops of water are caused to escape from the "water- 

 glands" on the teeth of the leaf-margin. A water-gland is a mass of 

 tissue at the end of a vein, communicating with the water-stomates on 

 the leaf-teeth. 



GLANDS- 



WATER " 



Fig. 44. Mode of demonstrat- 

 ing the Excretion of Fluid 

 Water from Leaves. 



