; Morphology and Life-History 7 



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oogonium then swells to a circular shape, and a second series of 

 hyphae, internal to the first, grow up in a similar manner. The 

 hyphae of both series branch and intertwine, completely growing 

 together, and forming finally a pseudo-parenchymatous tissue. A 

 number of branches grow from the internal layers of this primary 

 coat towards the interior of the developing perithecium and, re- 

 peatedly branching, fill up all interstices. The cells of these 

 branches, which are very rich in protoplasm and contain several 

 nuclei, disappear in the course of the growth of the perithecium, 

 becoming absorbed by the developing ascus or asci. The cells of 

 the outer layers become greatly flattened, and lose their protoplas- 

 mic contents, the external ones becoming dark brown and forming 

 the outermost wall of the perithecium. 



The oogonium after fertilization is known as the carpogonium, 

 and undergoes certain changes, which vary slightly according as 



one or several asci are formed. 



In Sphaerotheca, where a single ascus is found, the following 

 growth takes place. At about the time when the two primary 

 layers of hyphae have grown up from the stalk-cell, the carpo- 

 gonium begins to elongate, and nuclear division takes place, result- 

 ing in the formation of a single, more or less curved row of five 

 ix cells. In the penultimate cell of this row J:wo large nuclei 

 are always present, while the other cells contain only one each. 

 This penultimate cell is the young ascus. It swells strongly, so 

 that the apical cell of the series is pushed aside and downwards, 

 and finally absorbed. The two nuclei now fuse, and the ascus 

 rapidly increases in size, pressing together and flattening the cells 

 of the inner layers of the young perithecium. The nucleus in- 

 creases in size, and finally divides three times, providing the nuclei 

 for the eight ascospores which are subsequently produced by free- 

 cell formation. \xi Erysiphe,\^\\&x^ several asci are produced in 

 the perithecium, the development is, with slight modifications, the 

 same as that of Sphaerotheca (see Harper (i6i)). • 



, The fusion of the nuclei in the young ascus is evidently to be 

 regarded as a vegetative one, similar to that which occurs in 

 basidia, cystidia, and the asci of the other fungi— even some- 

 times, according to Massee (240), in the hairs of some of the 

 Discomycetes. Dangeard (96) however; regards the fusion of 



or ; 



