Cuttings rooted on H2O. Took 2 months to develop roots of 2 to 5 cm. These are Eurphorbia resinifera but also other Euphorbia species root well in water. Ideal temperature is around 20 degrees Celcius (=68 F). Just started an experiment with 2 
Lophocereus species. Keep you updated.
The reason for this experiment is that there is an overseas demand for this rooted plant material and as it’s a regulation that no soil particle is allowed to leave the country.. (etc. etc.). At this stage we are rooting a few hundred Euphorbia cuttings (diverse species) in water.
We are no scientists (just make use of them) but we like to experiment and prefer to choose for the most unlikable things. Sometimes we succeed, sometimes not but when you never try you will never know.
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Soekershof; the scientific backup 