14 EXPERIMENTAL PLANT PHYSIOLOGY. 



EXPERIMENT i6. 



OSMOSE IN PLANT-TISSUES. 



Hollow out the central part of a large Carrot, making the walls 

 of the cavity formed about. 5 cm. in thickness. Fill the cavity with 

 dry sugar. Twenty-four hours later the sugar will be dissolved in 

 the sap which is drawn into the cavity, while the Carrot is dry and 

 shrunken. 



12. Diffusion through Epidermis of Aerial Organs. — Roots and 

 root-hairs are pre-eminently organs of absorption, yet in some 

 instances leaves and stems exercise this function. The leaf- 

 like organs of Mosses and Liverworts are capable of absorbing 

 water. 



EXPERIMENT 17. 



WATERPROOFING OF LEAVES. 



Cut off a leaf of the Cabbage, Oak, Beech, or Iris and immerse 

 in water. The surface takes on a silvery appearance, due to the 

 thin layer of air adhering to it. An examination will show a 

 heavy layer of cuticle or waxy substapce on the outer side of the 

 epidermis. 



EXPERIMENT 18. 



ABSORPTION OF WATER BY LEAVES. 



Cut off a young branch of Coleus, Geranium, Tomato, Impatiens 

 or other convenient plant and seal the end with wax or gum. Lay 

 aside until slightly wilted. Immerse entirely in a vessel of water. 

 Examine in two hours. If the leaves are capable of absorbing 

 water, they will be restored to their original condition. It will be 

 found that few plants can take water by means of the leaves. A 

 moist atmosphere prevents loss of water, but does not form a source 

 of supply for the plant. 



13. Power of Selection of Food-material. — The root-hairs are 

 immersed in a solution of mineral salts in the soil in a manner 

 similar to the thistle-tube in Experiment 14. By the laws of 

 diffusion all of these substances should be absorbed bo the 

 root-hairs until an osmotic equilibrium is established, and gen- 



