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Lycoperdon pyriforme           Pear-Shaped Puffball

If you find a small puffball growing on a log or stump nine times out of ten (or better) it will be Lycoperdon pyriforme.  The other small puffball on logs is Morganella subincarnata.  This latter species is not pear-shaped (i.e. it has no sterile base) and the fruitbodies are wider than tall.

The fruitbodies of L. pyriforme are spiny when young.  As they age,  the spines (= outer peridium) wear off and expose a thin, membranous inner wall (= inner peridium).    When a falling raindrop strikes this membranous wall it causes an implosion that has a "bellows" action and a cloud of spores is puffed through the pore at the apex of the spore sac.  This can happen repeatedly throughout the summer.   Thus, the puffballs by its design,  has "arranged" to have its spores distributed when there is enough moisture around to favour spore germination and establishment at new sites for growth.  Neat!