PUFFING IN THE DISCOMYCETES 231 



explode readily when their tips are allowed to come into contact 

 with iodine or certain other poisonous substances such as mercuric 

 chloride, silver nitrate, copper sulphate, sulphuric acid, and alcohol ; 

 and I further showed that asci which have contracted considerably 

 owing to withdrawal of water from their vacuoles by potassium 

 nitrate, etc., explode when brought into contact with iodine. As a 

 result of these experiments I suggested that puffing is caused by a 

 stimulus given to the protoplasm in contact with the ascus lid. 



In 1926, Ziegenspeck ^ reviewed the literature upon, and gave 

 an account of his own investigations upon, the discharge mechanism 

 of the asci of Ascomycetes (Discomycetes, Pyrenomycetes, Lichens). 

 He came to the conclusion that, in fruit-bodies which puff, sudden 

 slight changes in the environment of the asci, by setting up a sudden 

 slight increase in the tension of the wall where the wall is weakest, 

 cause the asci to explode. Ziegenspeck regards the breaking open 

 of an ascus during the phenomenon of puffing not as being due to 

 the action of a stimulus but as a |Ji(re/^ mechanical phenomenon 

 comparable with the breaking of glass in which strains have been 

 set up by unequal heating or cooling : there is a zone or line of weak- 

 ness at the end of the wall of each ascus ; when the distension of an 

 ascus wall has become great, it needs only a slight additional strain 

 to cause the wall to break ; a very slight shaking, a very slight 

 warming, a very slight external pressure, or a sudden withdrawal 

 of water and therewith a reduction of elasticity, can lead to a sudden 

 increased strain inside the membrane, with the result that the 

 membrane relieves itself by splitting where its cohesion is least. 

 Ziegenspeck, by employing a microscope with special optical 

 arrangements, obtained evidence that strains are actually set up 

 in the walls of the ends of the asci of Peziza, Ascobolus, etc., just 

 before the asci explode. On looking down on ripe moist asci, their 

 ends appeared smooth and shining ; but, as soon as the asci were 

 blown upon, the ascus tips became iridescent and exhibited Newton's 

 rings. Immediately after showing these signs of strain, the walls of 

 the asci broke open and the spores were discharged. 



Ziegenspeck's explanation of the cause of the bursting of 



^ H. Ziegenspeck, " Schlcuderraechanismen von Ascomyceten," Botanisches 

 Archiv (Herausgeber, Carl Mcz), Bd. XIII, 1926, pp. 341-381. 



