The Erysiphaccae of Nebraska 5 



While the two primary wall layers are being formed, a row 

 of from three to six cells (Plate I, fig. 10) is formed by the 

 elongation and the division of the carpogone. In the penultimate 

 cell of this row there are two nuclei which soon fuse. Then 

 this cell, which is to become the ascus, rapidly increases in size 

 (Plate I, fig. 10), absorbs the apical cell and many of the sur- 

 rounding cells, its fusion nucleus divides to form the spores 

 (Plate I, fig. n), and finally the ascus with its contained spores 

 becomes mature. In the poly-ascus genera the sequence in this 

 process is essentially as has been given above. The only marked 

 variation is of course seen in the formation of more than one 

 ascus upon the division of the carpogone, a detail which need 

 not be considered in this place. 



The asci are colorless sacks. They are sessile or often some- 

 what pedicellate, globose, ovate, or cylindrical in shape (Plate I, 

 fig. 12) and from one to sixty or more in number. They con- 

 tain from two to eight spores which are also colorless. The 

 spores are continuous, with granular contents, oval or oblong, 

 and 15-34 X 8—25/* in size. Sometimes the ascospores do not 

 ripen until the spring following their first appearance upon the 

 host. They are incapable of immediate germination, apparently 

 demanding a resting stage of several months duration before they 

 will germinate. The germination of the ascospores (Plate I, fig. 

 1) and the development of the mycelium from them is very 

 similar to that process in the case of the conidia. Because of the 

 rather low percentage of germination of the ascospores they are 

 not nearly so effective in the rapid spread of the fungus as are 

 the conidia. The appendages on the perithecium are merely 

 extensions of certain cells in the outer wall (Plate I, fig. 11) of 

 the perithecium. Sometimes the perithecia when crushed emit 

 instead of the usual contents, a stream of small oblong spores 

 6.5-10 X 3-5-6)". in size, immersed in a colorless granular ma- 

 terial. In such cases there may usually be found on the same 

 mycelium smaller perithecia-like bodies which are oval or pyri- 

 form in shape and which contain the same kind of spores. These 

 are the fruits and spores of an imperfect fungus, Ampclomyccs 



63 



