A NOVEL METHOD OF ASCOSPORE 

 DISCHARGE 



D. Atanasoff 



It has been generally observed that ascospores are discharged 

 commonly from the apex of the ascus which ruptures at this point 

 just before the ascospores are liberated. A few forms, such as 

 Claz'iceps, have also been reported where the ascospores are dis- 

 charged through the lower end of the ascus when it is torn from 

 the perithecial base. A still different method of ascospore dis- 

 charge, however, has recently been observed in certain Pyreno- 

 phora species. These have developed on the leaves and stems of 

 Bromus and Agyropyron repens which earlier showed Heimin- 

 thosporiiim lesions and are regarded as the perfect stages of these 

 Helminthosporium species. Pleospora herbarum (Pers.) Rab., 

 studied on various hosts has shown the same phenomenon. In 

 these cases, the ascospore discharge is preceded by a modification 

 of the ascus and the spores are then liberated from the side of 

 the ascus. 



Upon placing a mature perithecium having fully developed asci 

 and ascospores in a drop of water on a microscope slide, the asci 

 are readily liberated by slight pressure upon the perithecium wall 

 and the ascospore discharge can be studied under the low power 

 lens. The ascus wall in these species consists of two layers, the 

 outer of which is thinner but more firm ; the inner, much thicker 

 and less firm. These two walls are not distinguishable, however, 

 until the moment of ascospore discharge. When the ascus is 

 liberated from the perithecium it begins to imbibe water. This 

 seems to take place so rapidly that in a few seconds the ascus 

 swells to one and one half times its original size. The pressure 

 on the outer wall soon becomes so great that the latter ruptures 

 at the apex of the ascus, contracts, and slips down toward the 

 base with great rapidity. In some cases, however, all of this 

 occurs less rapidly and can be easily followed under the micro- 



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