i 9 4 



MOVEMENTS AND EXCHANGES OF FLUIDS 



from the lower end of the twig. If the lower end of the twig is 

 also sealed and the suction applied before water has had time 

 to penetrate the lenticels immersed, the air may be forced out 

 through the lenticels on the lower end of the twig. The bottle 

 should be completely full of water in this test. If a short sec- 

 tion of a branch is sealed at both ends, then laid in a dish 

 of water and warmed slowly, the heated and expanding air may 



Fig. 95. Lenticel from branch of Coriaria myrtifolia, one year old. ff, restraining 

 layers, complete and unbroken, ff, beginnings of formation of restraining layer, phd, 

 phelloderm. After Devaux. 



be seen escaping from the lenticels. Seasonal variations in the 

 readiness with which lenticels conduct air are to be found. In 

 some species they are nearly closed in winter. 



268. The Length of Free Passages in Vessels. The vessels of a 

 plant show extremely long sections of lumina free from septae, 

 and by lateral connections furnish a free air passage for long dis- 

 tances in stems. The length of such segments may be demon- 

 strated as follows : prepare sections of branches of Salix, Populus, 

 or Syringa 20 to 50 cm. long, and lay in a trough of water. 



