BASIDIA AND THE DISCHARGE OF SPORES 25 



weakened up to a certain point, the hydrostatic pressure in the 

 hilum causes an explosion, so that the spore is shot from its 

 sterigma. The explosion, owing to its localisation at- the top of 

 the sterigma, does not involve the whole basidium. Further, we 

 must suppose that the amount of water liberated by the hydro- 

 static explosion at the tip of the sterigma is so minute that, even 

 with a microscope, there is little hope of our ever perceiving it. 



I do not feel that this theory is altogether satisfactory, but 

 have brought it forward as a basis for further discussion of the 

 whole question. The absolute constancy of the preliminary ex- 

 cretion of a drop seems to make it certain that the drop plays an 

 essential part in preparation for spore-discharge. I have assumed 

 that the drop is useful in that it acts upon the hilum-membrane 

 from without and thus weakens it prior to discharge. However, 

 in Pilobolus and the asci of Ascomycetes, the membrane which 

 breaks is weakened from within and no drop analogous to that 

 excreted by the hilum of the basidium is ever produced. No 

 support for my supposition as to the function of the drop can be 

 obtained from the Phycomycetes or the Ascomycetes. 



I have suggested that the drop acts either chemically or physi- 

 cally on the wall on which it rests and thus weakens it in preparation 

 for spore-discharge. Possibly, however, the growth of the drop 

 only accompanies such a weakening of the wall and is not the cause 

 of it. The excretion of drops from the pileal hairs of Coprinus 

 ephemerus, Psathrella disseminata, the cystidia of Inocybe tricho- 

 spora, and the sporangiophore of Pilobolus, etc., has, as already 

 pointed out, been shown by Knoll to be accompanied by the 

 mucilaginisation of those small portions of the outer part of the 

 cell- wall from which the drops arise. Judging by analogy, there- 

 fore, it seems not only possible but even probable that, whilst 

 the hilum-drop is being excreted, the wall joining the sterigma 

 and spore is undergoing change perhaps mucilaginisation and 

 is thus becoming weakened in preparation for spore-discharge ; 

 and that, as soon as this weakening has attained a sufficient degree, 

 the explosive force in the sterigma causes the spore to be shot 

 away. It may be that the supposed mucilage, as it is being formed, 

 pulls water from the sterigma by its force of imbibition and thus 



