Basidium

For instance, rust fungi in the order Puccinales have phragmobasidia with four cells that are separated by walls along their cross section.

Basidia with a short and narrow base are shaped like an inverted egg, and occur in genera such as Paullicorticium, Oliveonia, and Tulasnella.

Important factors in forcible discharge include Buller's drop, a drop of fluid that builds up at the nearer tip (hilar appendage) of each basidiospore; the offset attachment of the spore to the extending narrow prong, and the presence of hygroscopic regions on the basidiospore surface.

When a basidiospore matures, sugars present in the cell wall begin to serve as condensation loci for water vapour in the air.

At the pointed tip of the spore (the hilum) closest to the supporting basidium, Buller's drop builds up as a large, almost spherical water droplet.

Remarkably, the initial acceleration of the spore is estimated to be about 10,000 g.[2] Some basidiomycetes do not have a means to forcibly expel their basidiospores, although they still form them.