There are quite a number of tuberous cacti, so we can indeed consider them
to be in a
family of bulbs.

Even large cactus seeds need light to germinate properly. Almost all
cactus seed floats,
which perhaps aids in dispersal, and not much floating seed is buried for
sprouting in
habitat.

Uebelmannia gummifera sprouts and grows under white quartzite sand for
several years
before emerging. Its tiny seeds easily fall through cracks in adjacent
sand particles,
and its habitat on a slope of sand ensures there will be no flooding to
carry seed to a
less favored substrate. The sand transmits a lot of light, which one may
see by putting
a few millimeters of such sand in a transparent dish and looking up
through it at a
light.

Along with light, another requirement for cactus seed sprouting is
constant wetness, not
dampness. In this cacti are also like dry-area bulbs.

Leo Martin

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