192 SPORE DISSEMINATION 



perithecium. It was first correctly described by Pringsheim 

 (1858) from observations on Fleospora scirpicola (Sjphaeria 

 scirpi). Since then this type of discharge has been observed by 

 numerous mycologists in various genera, and the accounts of 

 Hodgetts (1917), Weimer (1920), Atanasoff (1919), Ingold 

 (1933, 1939), and Butler (1939) may well be consulted. In her 

 account Butler lists the following fungi as having jack-in-the-box 

 dehiscence: Ascospora beijerinckii, A. ruborum, Cucurbit aria 

 laburni, Lecanidion atratum, Leptosphaeria acuta, Metasphaeria 

 asparagi, Mycosphaerella rubina, Fleospora herbarium, Pl&wrightia 

 ribesia, Physalospora malorum, Sphaeria inquinana, S. ellipsocarpa, 

 S. lanada, S. lemaneae, Sporormia bipartis, and Venturia iuaequalis. 

 Such dehiscence has been noted in many other pyrenomycetous 

 £enera and also in several discomycetous ones. 



The essential structure that makes this type of discharge pos- 

 sible is the double ascus wall, consisting of an outer, thick, fairly 

 riqid, inextensible membrane, sometimes called the ectoascus, and 

 an inner, thin, elastic membrane, the endoascus. It may be im- 

 possible to distinguish the membranes as entities until the moment 

 discharge is begun. At maturity the ascus imbibes water as the 

 result of transformation of stored olycooen into osmotically active 

 compounds. Endosmosis occurs, but the outer ascus membrane 

 does not permit any considerable stretching to increase the di- 

 ameter. Enlargement proceeds to the point where the ectoascus 

 is ruptured, whereupon the endoascus suddenly elongates to one 

 to three times its original intact length. 



There are several types of rupture of the ectoascus. In Lecani- 

 dion atratum the tip of the ascus is lifted off, forming a thimble- 

 like cap at the tip of the endoascus. The remainder of the ecto- 

 ascus slips down toward the base of the ascus, or its edge is 

 folded or rolled as stockings are by some wearers. 



In Mycosphaerella a thin place may appear in the ectoascus 

 wall, in some species near the tip, in others well down along the 

 side. Rupture takes place at this thin area when sufficient in- 

 ternal pressure has been developed, and the ectoascus tip persists 

 as a flap at the side of the extended endoascus. At any rate, the 

 sudden release of the endoascus permits its apex to spring through 

 the ostiole. If, as in Sporormia, the ascospores are to be dis- 

 charged simultaneously, the further increased pressure ruptures 

 the ascus tip, and the spores are squirted en masse. If, as is more 



