SPORE DISCHARGE AMONG ASCOMYCETES 193 



common, the spores are to be discharged successively, they be- 

 come compressed into a single row with long diameters lying in 

 the direction of the longitudinal axis of the ascus. Then a con- 

 tractile pore forms in the apex, and each spore is ejected endwise. 

 Discharge of the 8 spores requires a period of a few seconds to a 

 minute or two. While the first half of the ascospore of Mycos- 

 phaerella is passing through the contractile pore, its velocity is 

 diminished, and it has been observed to stop momentarily at the 

 constriction. Its rate of ejection increases as the second half 

 passes through the pore, and the spore is snapped into space, some- 

 what after the fashion of a watermelon seed when compressed 

 between the fingers. The next spore in line instantly plugs the 

 pore, and the process is repeated until all 8 are ejected. The 

 empty ascus then contracts, and its place is taken by another 

 mature ascus or complement of mature asci. 



A fourth type of discharge is exhibited, especially by long- 

 necked or rostrate Pyrenomycetes. In this type, as illustrated by 

 Gnomoma riibi, Ophiobolus careciti, Endothia parasitica, and 

 Ceratostomella ampallacea [Ingold (1939)], the asci at maturity 

 become detached and for a time remain free and intact within 

 the perithecial cavity. As more asci are formed from the stro- 

 matic tissue within the basal portion of the perithecium, they be- 

 come freed and displace those first detached. As a consequence 

 a stream of asci is squeezed into the long neck canal, the asci pass- 

 ing up in single file. In Ceratostomella ampiillacea the asci swell 

 quickly as soon as they protrude from the ostiole, the lower end 

 being firmly held by the rigid jaws of the ostiole. The ascospores 

 are dispelled by the bursting of the ascus, and the empty ascus is 

 pushed out by the next ascus in the series, and so on. In some 

 rostrate species, such as Linospora gleditsiae, the asci collect in a 

 mucoid droplet at the orifice of the ostiole and must be dissemi- 

 nated by water. 



Still another structural mechanism has been described in other 

 Pyrenomycetes. In Glomerella, for example, the ascus is apically 

 thickened, and exit is provided through a papillar perforation. 

 The ectoascus remains intact. As the intra-ascal pressure increases, 

 the thickened pore resists stretching, but the ascospores are 

 squeezed through the perforation. As each emerges at the tip of 

 the pore, it is snapped into space. 



