150 RESEARCHES ON FUNGI 



spores were observed to be discharged from the sterigmata in 

 precisely the same manner as that described. Similar results were 

 obtained with Marasmius oreades and Coprinus comatus. 



The small size of the basidia and the difficulty of seeing the 

 narrow neck of a sterigma where it is joined on to a spore, make 

 it extremely difficult to observe what physical change takes place 

 at the end of the sterigma at the moment of spore-discharge. 

 However, after consideration of all the observed facts, it seems to 

 me that some conclusion as to the mechanism of the process 

 may be drawn. 



The first theory of spore-discharge which we may consider 

 is, that the four spores are shot off the sterigmata owing to the 

 latter breaking at their ends and discharging drops of fluid 

 consisting of cell-sap driven out of the basidium by the contraction 

 of the cell-wall. 1 I fail to find any facts in favour of this con- 

 ception. No drops could be detected on the sterigmata or spores 

 immediately after discharge. The disappearance of the spores did 

 not lead to any observable collapse of the sterigmata or basidium. 

 A strong adverse argument may also be derived from the fact 

 that the spores are discharged successively. A basidium is unicel- 

 lular. If, when a spore was discharged, the sterigma broke across 

 and a drop of fluid was forced out, the hydrostatic pressure in 

 the basidium would be very considerably lessened. There would 

 be a puncture in the cell. Under such conditions it seems diffi- 

 cult to imagine how the pressure could be used again for the 

 successive discharge of the three remaining spores. 



It seems to me that the clue to explain the mechanism of 

 spore-discharge can be obtained from comparative studies in other 

 groups of fungi. In the Ascomycetes, e.g. Ascobolus, the spores 

 are evidently driven out of the ascus by the pressure of the cell- 

 wall upon the cell-sap. The end of the ascus suddenly breaks 

 open, the ascus collapses, and the eight spores are discharged 

 simultaneously along with the cell-sap. A similar mechanism is 

 to be found for Pilobolus and Empusa Muscee. There is, however, 



1 We may suppose by analogy with other plant cells that the pressure of the 

 cell-sap upon the protoplasm and wall of the basidium is due to the process of 

 osmosis, and amounts to several atmospheres. 



