104 HEART-ROT 



de.sircd direction. It is expressed botaiiically by saying 

 that the i)ores are ])Ositively geotropic, i. e. they grow 

 towards the centre of the earth. The necessit}^ 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 ^2000 (== 8^o)> 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 pro])ulsion is provided by 

 the turgidity of the basidium and the siDore, each of which 

 tends to bulge out the septum which separates them. The 

 fineness of the mechanism is due to the thimiess of the 

 sterigma and the consequoit 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 

 fi'om the pores they arc easily carried away by the wind. 

 They germinate at once, either in piue water or damp air, 

 or in ])utrient solution, and imder suitable conditions every 

 si)ore 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 sterigma. 



2. Conidiophore-'i arise in all cultures. They are borne 

 on esi)ecially bjoad hyi)luie, ^\hicll occur in grou])s in the 

 mycelium, niid liave tiie foi-m shown in fig. 43. They may 

 be sim])le 01 hjanclied, and have a few cross sei)ta, and the 

 whole conidiophore is somewhat reminiscent of that of 

 Aspergillus. The conidioi)hore is rather swollen at its apex, 

 and the conidia closely resemble the basidiospores. When 

 the conidia have been ejected the conidiophores are left 



