Spring.wmf (18300 bytes) Plant Physiology (Biology 327)  - Dr. Stephen G. Saupe;  College of St. Benedict/ St. John's University;  Biology Department; Collegeville, MN  56321; (320) 363 - 2782; (320) 363 - 3202, fax;    ssaupe@csbsju.edu

Spuds McSaupe Plays with Sponges

General:  The purpose of today's visit by Spuds McSaupe is to study soil water relations.  A cellulose sponge is a reasonable model for soil.  We will use the sponge to demonstrate saturated soil, field capacity, gravitational water, capillary water, and permanent wilting point (percentage).

Exercise 1.  Lessons from a Wet Sponge.  Soak a sponge in water.  Then, place the sponge on a rack and allow it to drain.  Squeeze out the excess water in the sponge.

Exercise 2.  Container Size and Plant Watering.  Thoroughly saturate two large sponges.  On a rack, lay one flat and stand the other on end.  After several minutes, squeeze the sponges into a funnel into beaker. 

Exercise 3.  Distribution of Water in Soil.  One frequent cause of houseplant death is over watering.  This exercise with use sponges to model the distribution of water in the soil.  Soak 10 sponges in water until they are completely saturated.  Remove and then stack them on a rack to drain.  After several minutes, remove each sponge from the stack in sequence and squeeze out the excess water into funnel in a large test tube in a rack.  Repeat with each sponge.  Note the amount of water obtained from each sponge and the distribution in the the column of sponges.


  1. Why do plants usually die when they are over-watered?
  2. Some plants such as water lilies and rice spend their lives in water.  How do they avoid the problems associated with over-watering houseplants?
  3. Riparian plants often must deal with flooding.  How do they manage?
  4. Why do gardeners sometimes place pebbles or broken flower pot shards in the bottom of a pot?
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Last updated:  02/16/2009     � Copyright  by SG Saupe