The developing fruits of Cocos nucifera and Phoenix dactylifera as physiological sinks importing and assimilating the mobile aqueous phase of the sieve tube system

Analyses of ripe fruits of Cocos nucifera and Phoenix dactylifera carried out at the author’s laboratory, and data on the composition of the developing fruits of these palms derived from literature, have been used in a study which has shown that at any stage of its development the fruit may be regarded as being built up from a hypothetical fluid with an approximately constant composition. The composition of this assumed nutrient fluid, which could be postulated for its dry matter, total ash, K, Mg, Ca, P, and N contents, appeared to be very similar to that of the sieve tube exudates from severed inflorescences of Cocos nucifera and Arenga saccharifera (Palmae) and Yucca flaccida (Agavaceae). The only exception appeared to be the calcium content of the fruits, which was found to be at least 10 times higher than in an equivalent amount of sieve tube exudate. 90% or more of this calcium was localized in the vascular bundles of the husk and is assumed to have a xylem origin. The total amounts of phloem exudate solutes, which are annually obtained by palm-sap collectors from the stumps of cut off inflorescences, are of the same order of magnitude as the amounts normally utilized for the production of fruits. Fruit production, and exudate production may therefore be regarded as alternatives in utilizing the mobile aqueous phase of the sieve tubes system, which carries the available photosynthates and ions to either developing fruits or bleeding site. Since during fruit development the assimilates flow simultaneously to about 10 bunches of growing fruits, while a bleeding Cocos tree produces its exudate from about 10 successive inflorescences, the rate of mass transfer through one inflorescence will be about 10 times higher during bleeding than during fruit production. The data reported in this study are believed to deliver additional evidence for the view that mass flow is the way in which assimilates move through the sieve tubes into the growing fruits of Cocos nucifera, Phoenix dactylifera, and probably other palm species too.