Studies on Phloem Exudation from Yucca flaccida Haw. I. Some observations on the phenomenon of bleeding and the composition of the exudate

Alter young infiorescent stalks of intact, actively transpiring Yucca flaccida „ „ Haw. plants were wounded an exudate was obtained. Its flow continued for several weeks provided there was regular re-wounding. The exudate had a pH of 8.0-8.2 and contained about 18 per cent of total solids. Of these, sucrose constituted about 80-90 per cent. Glucose and fructose were minor constituents. The amino acid concentration was as high as 0.07 molar. Glutamine appeared to be the main nitrogenous constituent. The exudate only contained small amounts of inorganic solutes of which potassium was the main kation. The calcium content was relatively low. There appeared to be a great similarity between this phenomenon of bleeding and the composition of the exudate and that observed by one of the authors (P.M.L.T.) in previous years in several palm species. Various arguments are adduced in favour of the view that the exudate has a phloem origin.