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Noland, Lowell E. (ed.) / Transactions of the Wisconsin Academy of Sciences, Arts and Letters
volume XXVI (1931)

Wentzel, Erna A.
Morphological studies of Erysiphe aggregata on Alnus incana,   pp. [241]-Plate IV ff. PDF (4.9 MB)

Page [241]

 The powdery mildews offer especially favorable material for the study of
the development of the perithecium. The following study was undertaken for
the purpose of extending our knowledge of the group by an account of the
development of the ascocarp and spore formation in the genus Erysiphe. 
 The structure of the ascocarp and the stages in its development have been
fairly well understood since the time of De Bary (1863) and the main points
of his conclusions have been many times confirmed. 
 In his investigation of Sphaerotheca castagnei De Bary (1863) found that
at the crossing point of two hyphae, or at the place where two neighboring
hyphae touch, each hypha develops a small upright branch which is soon cut
off by a septum from the parent hypha. One of these branches swells to an
oval-oblong shape and becomes the oogonium. The other lengthens slightly
and applies itself closely to the side of the oogonium, curving above itso
that its end lies on the apex. The upper part is then cut off by a septum
and forms the antheridium. 
 De Bary observed no breaking down of the wall between the antheridium and
oogonium and so supposed that no con-. jugation took place; nevertheless
he considered that these organs represented a true sexual apparatus and that
the perithecium subsequently formed was to be regarded as the result of a
sexual act. This last conclusion has been verified by the works of Harper
and others. 
 Harper (1895) described the sexual apparatus for Sphaerotheca castagnei,
Phyllactinia corylea, Erysiphe communis, and E. cichoracearum, and found
them to arise in general in the same manner. He observed that the sexual
apparatus is formed where two hyphae cross or lie close beside each other,
thus the oogonium and antheridium arise as lateral branches from separate
hyphae. , , 

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