66 RELATIONS OF PLANTS TO WATER 



some forms of metabolism continue until desiccation reaches a 

 point where disorganization ensues. 



These manifold relations of water to the organism give it a 

 potent influence in determining the form and structure of the 

 organs. The size of the individual, stature of the leaves, and 

 structure of the organs of absorption and transpiration respond 

 directly to the environmental water relations of the plant. 



101 . Effect of Desiccation upon Movement of Protoplasm. Select 

 a leaf of Philotria in which rapid movement of the strands of 

 protoplasm may be seen. Remove the cover-glass, exposing this 

 aquatic leaf to the air for a half hour. Re-cover, and add a drop 

 of water ; note time necessary for resumption of movement. Test 

 the extent to which this desiccation may be carried and the move- 

 ment resumed. 



102. Resistance of Seeds to Desiccation. A striking test of the 

 power of seeds to undergo desiccation may be made if a number 

 of seeds of the pea, wheat, corn and radish are placed in a small 

 glass tube sealed at one end. They should have been previously 

 dried in the sun for a week. Now connect the tube with a mer- 

 curial air pump and exhaust to the full capacity of the pump. 

 With the pump still in action, seal up the tube by cutting across, 

 or fusing it with a bunsen flame, taking care not to heat the seeds 

 unduly. A month later break the tube, and place the seeds in a 

 second tube and seal as before. Take the seeds from the second 

 tube at the end 'of a month and test germinating power. Gather 

 a half dozen kinds of seeds from tender herbaceous plants, grow- 

 ing in moist shaded situations, and place them in a desiccating 

 chamber using sulphuric acid to absorb moisture. Test the 

 germinating power of the desiccated seeds two weeks later. 

 Seed pans or some form of germinator should be used for these 

 tests (See also, Effect of vacuum upon seeds). 



103. Hydrotropic Reactions. Some plants have acquired a 

 specific irritability to moisture which enables them to direct ab- 

 sorbing, or other organs toward a greater intensity of this sub- 

 stance if the plant is not receiving its maximum supply, or away 



