24 EXPERIMENTAL PLANT PHYSIOLOGY. 



water in a dish. Cut off the stem under water, and it will remain 

 fresh several days if the cut end is kept immersed. At the same 

 time cut off another shoot in the air, and after 10 minutes place the 



FIG. 21. 



Excision of a shoot under water. (After Oels.) 



cut end in the vessel of water with the other shoot. Compare 

 results daily. (Fig. 21.) 



19. Conditions of Transpiration. Plants transpire water con- 

 stantly over their entire aerial surface, yet the stems and the 



FIG. 22. 



c 



Stoma from under side of leaf of Iris florentina. c, cuticle. (Strasburger.) 



greater part of the leaves are covered with an almost impervious 

 layer of cuticle. Beside this, the devices exhibited by plants, 

 especially those growing in the drier regions, by which trans- 



