-104- MECHANICAL STRUCTURE. 



78. Turgor. 



(a) Young seedlings droop owing to loss of turgor when immersed in a salt solution 

 having a higher osmotic pressure than that of their cell-sap. 



(6) Older seedlings do not droop under the same circumstances owing to the 

 presence of rigid supporting tissue. 



79. Plasmolysis. Living cells seen under the microscope: (a) in water, and 

 (6) in a solution of higher osmotic pressure than that of the cell-sap. 



80. Disposition of supporting tissue. 



(a) Comparison of longitudinal and transverse sections of stem and root to 



show relative positions of supporting tissue 



(b) Section of a leaf to show girder structure of supporting tissue. 



