In fungi, both asexual and sexual spores or sporangiospores of many fungal species are actively dispersed by forcible ejection from their reproductive structures. This ejection ensures exit of the spores from the reproductive structures as well as travelling through the air over long distances. Many fungi thereby possess specialized mechanical and physiological mechanisms as well as spore-surface structures, such as
hydrophobins, for spore ejection. These mechanisms include, for example, forcible discharge of ascospores enabled by the structure of the ascus and accumulation of
osmolytes in the fluids of the ascus that lead to explosive discharge of the ascospores into the air. The forcible discharge of single spores termed
ballistospores involves formation of a small drop of water (
Buller's drop), which upon contact with the spore leads to its projectile release with an initial acceleration of more than 10,000
g. Other fungi rely on alternative mechanisms for spore release, such as external mechanical forces, exemplified by
puffballs. Attracting insects, such as flies, to fruiting structures, by virtue of their having lively colours and a putrid odour, for dispersal of fungal spores is yet another strategy, most prominently used by the
stinkhorns. In Common Smoothcap moss (
Atrichum undulatum), the vibration of sporophyte has been shown to be an important mechanism for spore release. In the case of spore-shedding
vascular plants such as ferns, wind distribution of very light spores provides great capacity for dispersal. Also, spores are less subject to animal predation than seeds because they contain almost no food reserve; however they are more subject to fungal and bacterial predation. Their chief advantage is that, of all forms of progeny, spores require the least energy and materials to produce. In the spikemoss
Selaginella lepidophylla, dispersal is achieved in part by an unusual type of
diaspore, a
tumbleweed. == Origin ==