SPHAERIALES 283 



side of the opening of the original pycnium p x a second external false 

 pycnium p 2 . The pycniospores of the former are larger and thicker than 

 those cut off on the upper surface. The stromata develop further as in 

 Diatrype disciformis. First an entostroma is laid down which serves as 

 the site of perithecial formation. In contrast to D. disciformis, however, 

 the upper part of the entostroma is not differentiated into marked scleren- 

 chymatic placodium, so that the connection of both stromatal layers is 

 not so roughly interrupted. The perithecial necks gradually push out 

 through the ectostroma and help to raise the dark brown layer which has 

 meanwhile died. Finally all the stromatal substance blackens. 

 Whether sexual acts occur in the perithecia is not yet determined histolo- 

 gically; possibly they are present, as in certain strains of Diaporthe 

 perniciosa there is a peculiar physiological sexual differentiation (Cayley, 



1923). 



Apioporthe anomala has a strongly developed stroma, like that of 

 Diatrype, and unequal two-celled spores. Apioporthe obscura has a well- 

 developed stroma about the perithecia, although it is not as erumpent 

 as in A. anomala. In A. phomospora, this entostromatic development 

 shows a still greater reduction, with only a slight development of myce- 

 lium about the perithecia and a slight blackening of the bark surfaces 

 above them. Conidia are produced in stromata by the breaking up of 

 the mycelium (Wehmeyer, 1928). 



Parallel to the Diaporthe group, we find a second sub-series which does 

 not produce a dark marginal zone, at least not until late in the history of 

 its development. In Melanconis the stromatic development is limited to 

 an ectostromatic disc and the perithecia are imbedded in the unaltered 

 cortex. The ascospores become colored and uniseriate in the ascus, but 

 remain two-celled. The imperfect stage is a typical Melanconium with 

 the conidia borne in the shallow cavities on the sides of a sterile disc, or 

 over the entire surface of a hemispherical ectostroma. 



Melanconis stilbostoma is fairly common on the dry twigs and pieces 

 of stem of Betula alba. Under the periderm, it forms a fibrous cell 

 complex which arches out to a head (Fig. 185, 3) and cuts off over its 

 whole surface, dark-walled conidia of Melanconium bicolor. On account 

 of the formation of conidia on flat or pulvinate layers, Melanconis is 

 usually regarded as the type of the Melanconideae and hence contrasted 

 to the Valsaceae in the narrower sense, which form conidia in pycma. 

 Frequently the fungus, especially in unfavorable weather, does not attain 

 this conidial stage, but transforms its pseudoparenchyma into a sclerotic 

 tissue. 



In contrast to the previous genera, the entostroma remains mycelial 

 and does not develop to an independent stromatal layer. The necks of 

 the perithecia grow through the whole ectostroma, whose outer layer 

 changes into a rind-like placodium (Fig. 185, 4). While in Diatrype the 



