Phloem exudation from castor bean: Induction by massage.
Exudation can be induced or greatly enhanced in Ricinus by massaging the stem periodically some time before tapping the sap by making an incision. Nevertheless temporary massage during exudation stops flow completely indicating that flow is prevented normally by a pressure sensitive sealing mechanism which becomes desensitised by regular massage.
Botany Department, University of Glasgow, Scotland.
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JA
Milburn