SPORE DISCHARGE AND DISSEMINATION 343 



rangia are eaten by beetles, which in turn are eaten by frogs or hzards. 

 After the beetles are digested and the sporangia are released, the spores 

 are formed. These spores are then capable of germination and produc- 

 tion of mycelium on frog or lizard excreta. 



A somewhat different method of discharge is described for the genus 

 Entomophthora by Fitzpatrick (1930) and more specifically for E. sphaero- 

 sperma by Sawyer (1931). Instead of being due to a squirting action of 

 the cell contents, as in the case of Piloholus and Bastdiobolus, the discharge 

 of the sporangium in Entomophthora involves the opposing forces of 

 osmotic pressure and the adhesive power between the two walls separating 

 the sporangium and sporangiophore. As the sporangium matures, the 

 pressure on both sides of the separating walls becomes so great that the 

 outer wall is suddenly broken, and the sporangium is thrown into the 

 air. The sporangia, being sticky, readily adhere to the objects which 

 they strike. 



The theory of violent discharge of sporangia in certain downy mildews 

 was advanced by De Bary (1887), using Peronospora parasitica and 

 Phytophthora infestans as examples. Later, Pinckard (1942) found the 

 forcible adiection of sporangia in Peronospora tabacina to be the same as 

 that described by De Bary. As the mature sporangiophore dries out, 

 the entire crown, with its branches and sporangia, begins a counterclock- 

 wise rotation. Each portion of the sporangiophore, including the 

 sterigma, rotates independently. The sporangiophore is hygroscopic, 

 and as the air becomes more moist, the movement is reversed. The effect 

 is a sudden release of the mature sporangia. During the course of rota- 

 tion many of the branches become entangled with others, and the spo- 

 rangia are dislodged by the spring-like action as the branches are dis- 

 engaged. The discharge of sporangia was verified by observations on 

 single isolated sporangiophores, showing that it is not dependent upon 

 the intermingling of the sporangiophores. No sporangia were released 

 in a saturated atmosphere, since no hygroscopic movement took place. 

 Other species which were observed to react similarly were Peronospora 

 parasitica, P. geranii, P. halstedii, and P. effusa. Similar rotation of 

 conidiophores upon desiccation is apparently not uncommon among fungi 

 of other groups, particularly those with long conidiophores. 



Discharge of ascospores. In the majority of fungi (except those whose 

 asci deliquesce), ascospore discharge is accomplished by the building up 

 of osmotic pressure of the ascus to a point where it exceeds the resistance 

 of the elastic ascus wall. In one type of expulsion, the ascus wall is 

 suddenly ruptured, usually throwing the ascospores outward into the air 

 simultaneously. In other species, the ascospores are discharged succes- 

 sively through an apical pore in the ascus. In the latter case, the ellipsoid 

 or fusoid shape of the spore is apparently important. The spore pushes 



