In many cases the colour-production is dependent on certain definite conditions - temperature, presence of oxygen, nature of the food-medium, &c. Ewart's important discovery that some of these lipochrome pigments occlude oxygen, while others do not, may have bearings on the facultative anaerobism of these organisms.
Similarly we are unable to divide Schizomycetes sharply into parasites and saprophytes, since it is well proved that a number of species - facultative parasites - can become one or the other according to circumstances.
Their metabolic products may induce blood-poisoning or other toxic effects (facultative parasites) though they are not true parasites.
The provisions of neither convention are obligatory, but merely " facultative," amounting only to recommendations.
Since 1875, 1000 citizens can claim a popular vote (facultative Referendum) on all bills, or can exercise the right of initiative whether as to laws or the revision of the cantonal constitution.