Introduction to Fungi, Third Edition

NUMBERS OF BASIDIOSPORES
495
Fig18.7 Itersonilia perplexans. Appearance of Buller’s drop and adaxial drop. a 1
a 5
show events immediately preceding and following
the discharge of a secondary ballistospore. An adaxial drop is clearly seen. b 1
b 5
show drops developing on a primary ballistospore.
Note that there is no decrease in the size of the ballistospore as the drops develop. c 1
c 3
illustrate failure of ballistospore discharge.
Here coalescence of Buller’s drop and the adaxial drop is not accompanied by separation of the spore from its sterigma and the
spore soon topples from its perch. Reprinted from Webster et al. (1984a), with permission from Elsevier.
water or the sea, they do not produce ballistospores
there.
The spore of Itersonilia is subjected to considerable
acceleration and moves away from the
sterigma at a velocity of over 1 m s 1 . However,
the large surface/mass ratio of a relatively small
object like a ballistospore results in high wind
resistance and therefore rapid deceleration and
loss of momentum, so that the spore soon falls
under the preponderant influence of gravitational
force. The trajectories of ballistospores
of most fungi follow a short horizontal path
for a distance of about 0.1 0.3 mm and then
turn through a right angle so that spores in still
air drift downwards at a steady sedimentation
velocity. This characteristic trajectory, termed a
sporabola, ensures that basidiospores projected
into the space between the gills or into the
lumen of a pore turn vertically downwards
before hitting the opposing hymenial surface.
18.6 Numbers of basidiospores
The number of basidiospores produced by a
single basidiocarp can be extremely high. Buller
(1909) estimated that the detached cap of the