To obtain a reliable estimation on the yield of illicit indoor cannabis cultivation in The Netherlands, cannabis plants confiscated by the police were used to determine the yield of dried female flower buds. The developmental stage of flower buds of the seized plants was described on a scale from 1 to 10 where the value of 10 indicates a fully developed flower bud ready for harvesting. Using eight additional characteristics describing the grow room and cultivation parameters, regression analysis with subset selection was carried out to develop two models for the yield of indoor cannabis cultivation. The median Dutch illicit grow room consists of 259 cannabis plants, has a plant density of 15 plants/m(2), and 510 W of growth lamps per m(2). For the median Dutch grow room, the predicted yield of female flower buds at the harvestable developmental stage (stage 10) was 33.7 g/plant or 505 g/m(2).

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The effect of dark and light treatment on endogenous cytokinins in internodes and buds of Iris was determined. Plant material was purified by chromatographic methods and cytokinins were assayed by an immunoassay .An indirect competitive enzyme immunoassay for the determination of zeatin-and isopentenyl-adenine cytokinins was developed . This assay, which is not dependent on the titre of the antibodies raised against zeatin riboside and isopentenyl-adenosine appeared to be specific, highly sensitive and more reproducible compared to a direct competitive enzyme immunoassay for cytokinins .Isopentenyl-adenosine was the most abundant cytokinin found, followed by zeatin : the latter counteracts bud blast when injected into dark-treated plants . Smaller amounts of isopentenyl-adenine and zeatin riboside were found . Results are in agreement with the hypothesis that deficiency of growth substances like cytokinins plays an important role in the occurrence of flower-bud blasting.A possible role for the major endogenous cytokinin, isopentenyl-adenosine, which earlier was found not to be effective in counteracting bud blast when injected into buds of dark-treated plants, is discussed .

Flower-bud blasting in Iris occurs in the winter when low light intensities and short days prevail. After introduction of 14 CO, to one leaf the transport of assimilates was studied under controlled culture conditions in a control light treatment and in a treatment of 7 days darkness followed by standard light conditions . Little assimilate transport was found in the direction of the bud in dark-treated plants . However, zeatin injection into the flower buds of the plants subjected to the dark treatment clearly promoted assimilate transport to these buds. Abscisic acid levels, determined by gas chromatography, were found to increase in the buds of dark-treated plants . Zeatin injection into the flower bud resulted in a suppression of the abscisic acid level . The latter treatment also resulted in higher percentage of flowering . Removal of flower parts was found to inhibit peduncle elongation . The peduncle elongation of complete flowers started in a well defined period, and the fresh weight of buds was found to increase mainly in the last part of that period . Assimilate transport under low light intensities in relation to abscisic acid and supposed gibberellin is discussed .