THE MECHANISM OF SPORE-DISCHARGE 151 



another way in which the hydrostatic pressure may be used as a 

 driving force. This is illustrated in several Entoinophthorinea\ 

 In Empusa Grylli, according to Nowakowski, 1 the wall separating 

 the conidium from the basidium is double. There is a tiny colu- 

 mella projecting into the former. When the conidium is ripe, 

 the two walls separate by mutually bulging in opposite directions 

 in response to hydrostatic pressure both in the conidium and the 

 basidium. In consequence of the bulging taking place very 

 rapidly, the spore is shot forwards to some distance. It thus 

 happens that the basidium is not punctured in discharging its 

 spore, and therefore does not lose any cell-sap. The basidium 

 merely alters its shape. It becomes slightly enlarged terminally, 

 whilst doubtless contraction takes place laterally. Probably during 

 this process the hydrostatic pressure of the cell-sap upon the cell- 

 wall becomes slightly diminished. We have a process which 

 we may distinguish as the jerking discharge as opposed to the 

 squirting discharge of Empusa Muscse and Ascobolus, &c. 2 



It appears to me very probable that the four spores are dis- 

 charged from the basidia of Hymenomycetes by a jerking process 

 essentially similar to that just described. This hypothesis involves 

 the assumption of a double wall separating the sterigma and spore, 

 and that the two walls mutually bulge so as to press against one 

 another when spore-discharge takes place. That such a double wall 

 in each sterigma must be present seems to be proved by the fact 

 that both spore and sterigma are turgid after discharge. The 

 pointed " tail " of each spore and the pointed end of the sterig- 

 mata after becoming naked are facts in favour of the idea of a 

 mutual bulging of the two walls which were in contact. The 

 hydrostatic pressure in the basidium would be only very slightly 

 diminished as each spore was shot off and would be available 



1 Quoted from Die Pflanzen-familien of Engler and Prantl, who reproduce 

 Nowakowski's figures. Teil 1, Abteil 1, Entomophthorinese, p. 135. 



2 In Basidiobolus ranarum we have both squirting and jerking processes in 

 succession. The basidium first breaks across, and the outer end with the spore 

 is shot away by the squirting process. The spore is then shot off the collapsed 

 end of the basidium by the jerking process. The spore-wall at the place of 

 attachment bulges out so as to become pointed. In Conidiobolus utriculosus, 

 apparently, sometimes the squirting process is used and sometimes the jerking. 

 See Engler and Prantl, loc. cit. 



