Growth of the Lilium longiflorum pollen tube in vitro is restricted to a zone extending back 3–5 μ from the tip. Electron micrographs of cross and longitudinal thin sections of L. longiflorum and L. regale pollen tubes reveal that the cytoplasm of the nongrowing region of the tube contains an abundance of mitochondria, amyloplasts, Golgi bodies, endoplasmic reticulum, lipid bodies, and vesicles. In contrast, the growing tip is characterized by an abundance of vesicles and an absence of other cytoplasmic elements. The vesicles appear to be of 2 types. One is spherical, about 0.1 μ in diameter, stains strongly with phosphotungstic acid, apparently arises from the Golgi apparatus and appears to contribute to tube wall and plasmalemma formation. The other type is irregular in shape, 0.01‐0.05 μ in diameter, stains strongly with lead hydroxide, and is of unknown origin and function. Cytochemical analysis indicates that the tips of L. longiflorum pollen tubes are singularly rich in ribonucleic acid, protein, and carbohydrate. These findings are discussed in relation to tube growth.

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We have developed a radioimmunoassay (RIA) for abscisic acid (ABA) in the 0.1 ng to 2.5 ng range. Antibodies were obtained from rabbits immunized with ABA bound via its carboxyl group to bovine serum albumin. Cross-reactivity studies indicate that ABA esters are completely cross-reactive with ABA, while trans, trans abscisic acid (t-ABA) phaseic acid (PA) and dihydrophaseic acid (DPA) have much lower but significant cross-reactivities. Purification methods which reduce the levels of cross-reacting substances are described.