The better rooting performance of stump sprouts offers the means of mass‐producing rooted cuttings of many difficult‐to‐root genotypes. To study the physiological basis of rooting, stem cuttings were taken from stump sprouts of the more readily‐rooted hybrid poplar cultivar DN (P. deltoides × P. nigra) and the difficult‐to‐root aspen hybrid cultivar AE (P. alba × P. tremula). Seasonal variation in rooting percentage of both the AE and DN cultivars (higher in winter and lower in late summer and fall) of poplar was correlated with higher and lower levels of abscisic acid (ABA), respectively, in fractionated extracts of poplar. The presence of ABA in the purified inhibitory fraction was unequivocally confirmed by (i) co‐chromatography, (ii) gas chromatography‐electron capture detector and isomerization with UV light and (iii) combined negative chemical ionization‐mass spectrometry. Although ABA was identified in the inhibitory fractions of mung bean bioassays of both poplar and aspen extracts, exogenous ABA did not inhibit rooting when applied at physiological concentrations. Since ABA levels were higher in the more readily‐rooted hybrid poplar cultivar DN and were higher in February, close to the time of maximal rooting of cuttings, this suggests that ABA levels may possibly explain clonal and seasonal variation in rooting patterns of poplar stump sprouts. This interpretation is supported by the fact that lower, physiological concentrations increased rooting percentage, root number and root elongation when ABA was added to poplar and aspen cuttings.

SYNOPSISThe glyceride glycerol analysis depends, after saponification of triglycerides, on a linked enzymatic procedure using glycerokinase, pyruvate kinase, and lactate dehydrogenase: the final conversion of NADH to NAD+ is followed fluorimetrically. Twenty analyses can be performed per hour on the AutoAnalyzer; recoveries of added triglycerides ranged between 90 and 104 %. In a mixed male and female group the normal range for glyceride glycerol was 2 5 to 15 5 mg/100 ml (0-2-1-4 mmol/l) fasting, and 2-5 to 18-0 mg/100 ml (0.2-1-6 mmol/l) postprandially using fresh serum. There was a significant rise postprandially in older men.

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