Page:Life Movements in Plants.djvu/261

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RESUMPTION OF AUTONOMOUS ACTIVITY
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results described enable us to enunciate general Laws of Effects of Direct and Indirect stimulus on tissues in normal and in sub-tonic condition.

LAWS OF EFFECTS ON DIRECT AND INDIRECT STIMULUS.

1. THE EFFECT OF DIRECT STIMULUS IS NEGATIVE VARIATION OF TURGOR, NEGATIVE MECHANICAL AND ELECTRICAL RESPONSE, NEGATIVE VARIATION, OR RETARDATION OF RATE OF GROWTH.

  1. SUB-MINIMAL STIMULUS GIVES POSITIVE RESPONSE.
  2. POSITIVE RESPONSE IS ALSO GIVEN BY A TISSUE IN A SUB-TONIC CONDITION: CONTINUOUS STIMULATION CONVERTS THE ABNORMAL POSITIVE TO NORMAL NEGATIVE RESPONSE.
  3. AUTONOMOUS ACTIVITY IN A STATE OF STANDSTILL, MAY RE REVIVED BY STIMULUS.
  4. THE EFFECTS OF STIMULUS AND WARMTH ARE ANTAGONISTIC.

2. THE EFFECT OF INDIRECT STIMULUS IS POSITIVE VARIATION OF TURGOR, POSITIVE MECHANICAL AND ELECTRICAL RESPONSE AND POSITIVE VARIATION OR ACCELERATION OF RATE OF GROWTH.

I have referred to the fact previously demonstrated, that while Direct stimulus induces contraction and retardation of growth, moderate rise of temperature induces the opposite effect of expansion and acceleration of growth. Further demonstration of the antagonistic effects of stimulus and warmth will be given in the next Paper.

SUMMARY.

The autonomous activity of pulsating leaflet of Desmodium gyrans comes to a stop under depletion of internal energy. A cut leaf isolated from the plant maintains the

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