104 HEART-ROT 
desired direction. It is expressed botanically by saying 
that the pores are positively geotropic, i.e. they grow 
towards the centre of the earth. The necessity for exactitude 
in this orientation is demonstrated by the following calcula- 
tion. If a tube is 0-25 mm. across and bears spores for 
a distance of 2 cm. from the orifice, a displacement from 
the vertical of tan~*z235 (= do), i.e. a displacement of 
less than 1°, will prevent any spores growing as far as 2 cm. 
from the orifice from escaping (fig. 42). Actually the 
accuracy has to be far greater than is shown in this calcula- 
tion, since the spores do not simply fall from the basidia 
but are shot off to a distance of rather less than 0-1 mm. 
(vide Buller). The ejection mechanism for the Polyporeae 
has been investigated by Buller, and, as is shown in the 
accompanying diagram (fig. 41, B), the ejection is accom- 
plished by the splitting of the septum between the spore 
and the sterigma. The force of propulsion is provided by 
the turgidity of the basidium and the spore, each of which 
tends to bulge out the septum which separates them. The 
fineness of the mechanism is due to the thinness of the 
sterigma and the consequent small cross-section of the 
septum that crosses it. 
The spores, being very small, present a large surface in 
proportion to their weight, so that once they have escaped 
from the pores they are easily carried away by the wind. 
They germinate at once, cither in pure water or damp air, 
or in nutrient solution, and under suitable conditions every 
spore germinates. ‘The germ tube may emerge from any 
part of the wall, even, occasionally, from the small point 
where the spore was attached to the stcrigma. 
2, Conidiophores avise in all cultures. They are borne 
on especially broad hyphae, which occur in groups in the 
mycelium, and have the form shown in fig. 43. They may 
be simple or branched, and have a few cross septa, and the 
whole conidiophore is somewhat reminiscent of that of 
Aspergillus. The conidiophore is rather swollen at its apex, 
and the conidia closely resemble the basidiospores. When 
the conidia have been ejected the conidiophores are left 
