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140 3. Prolonged application of indirect stimulus of moderate in- tensity GIVES RISE to a DIPHASIC, POSITIVE MECHANICAL RESPONSE FOLLOWED BY THE NEGATIVE,

4. If the INTERVENING TISSUE BE HIGHLY CONDUCTING, THE TRANS- MITTED POSITIVE EFFECT BECOMES MASKED BY THE PREDOMIN- ANT NEGATIVE.

The laws of Effects of Direct and Indirect stimulus hold good not merely in the case of sensitive plants, but universally for all plants. This aspect of the subject will be treated in fuller detail in later Papers of this series.