50 PLANT PHYSIOLOGY AND ECOLOGY 



more rigid bundle and epidermal layer to compress the swollen 

 parenchyma and hence to increase its rigidity. In consequence, 

 turgidity becomes a fundamental factor in support. This is 

 particularly evident when stems and leaves are allowed to wilt. 

 The water is removed from the cells more rapidly than it is sup- 

 plied. The cells collapse, and with them the stem and leaves, 

 in spite of the support of the fibrovascular bundles. 



Turgidity is so intimately wrapped up with the absorption 

 of water and its diffusion by means of osmosis that plants can 

 function normally only while they are turgid. A temporary loss 

 of turgidity is usually not fatal, but all the functions dependent 

 upon water are necessarily brought to an abrupt stop. If the 

 flaccid condition continues for a long period, the power of the 

 plant to carry on absorption and diffusion is lost, and the plant 

 dies. In this connection, turgidity renders the indispensable ser- 

 vice of keeping the protoplasm firmly pressed against the cellu- 

 lose walls, a condition necessary for keeping the wall filled with 

 water. The latter in turn is absolutely necessary to the passage 

 of water through the wall, and hence to diffusion. Turgidity 

 is thus seen to furnish a ready clue to the condition of the plant. 

 Turgid plants are normal, flaccid plants abnormal, i.e., in a patho- 

 logical condition. 



Experiment 12. Demonstration of turgidity. Cut a 3-inch section 

 of dialyzer tubing and soak it in distilled water until softened. Carefully 

 fold and tie one end, fill with a 10% solution of common salt, and tie 

 the open end as closely as possible above the level of the liquid. Place 

 this artificial cell first in distilled water, and, after it has become fully 

 distended, put it in a 20% solution of common salt. Note the results. 

 Place the cell in soil saturated with distilled water colored by erythrosin, 

 and explain its behavior. 



Allow two sunflower plants to wilt. Water one as soon as the 

 leaves wilt strongly, and the upper part of the plant begins to droop. 

 Water the second only after the whole plant has collapsed. Explain 

 the results. 



TRANSPORT 



64. General nature. In all stemmed plants, the surface that 

 absorbs water is separated by a greater or less length of stem 

 from the leaf surface which loses water. Even in stemless flowering 

 plants, practically the same condition exists, since a similar separa- 



