280 CLASS ASCOMYCETEAE 



the host tissues except for the projecting ostiole. A crust-hke stroma 

 (clypeus) may in some cases connect the upper portions of the ascocarps. 



Family Gnomoniaceae. These are parasitic or saprophytic in the 

 leaves, stems, and other portions of vascular plants. The asci are usually 

 thickened above and with a distinctly visible pore. The necks of the 

 sunken perithecia project well above the surface. Many of the species are 

 parasitic and produce the conidia on the living tissues of the host but the 

 perithecia are produced only on the dead tissues. The conidia are usually 

 produced in acervuli, in gummy masses which are distributed by rain and 

 insects when wet but harden into a horny mass when dry. InGnomonia the 

 perithecia are not in a stroma. G. veneta (Sacc. & Speg.) Kleb. on the 

 plane tree or sycamore (Platanus) has various types of conidial forms 

 that have been described in the following form genera: Gloeosjporium, 

 Discula, Sporonenia, and Fusicoccum. This causes leaf scorch and leaf fall 

 and kills the twigs and sometimes the larger branches. Glomerella is like 

 Gnomonia except that the perithecia are embedded in a stroma. Gl. 

 cingulata (Stone.) Spauld. & von Schr. is found on a large number of 

 hosts and has for its conidial stage forms that have been described as 

 CoUetotrichum and Gloeosporium, depending upon the presence or absence 

 respectively of setae around the edge of the acervulus. This species 

 causes various forms of diseases: bitter rot of the apple {Malus), withertip 

 of the twigs and tearstain of the fruits of orange (Citrus), anthracnose of 

 mango (Mangifera) and avocado (Persea), etc. (Fig. 91 B-D.) 



The two families Pleosporaceae and Mycosphaerellaceae are in the 

 older classifications placed next to the foregoing. Their asci are not 

 thickened at the apex nor provided with a pore. The structure of the 

 ascocarp is such that these fungi must be transferred to the order Pseudo- 

 sphaeriales, where they are given consideration. 



In contrast to the foregoing families in which in the main the peri- 

 thecia are not immersed in the fungus stroma there is found a group of 

 fungi with varying degrees of stromatic development. Lindau (1897), in 

 Engler and Prantl's "Die Natiirlichen Pflanzenfamilien," divides these 

 organisms into five families: Valsaceae, Melanconidaceae, Diatrypaceae, 

 Melogrammataceae, and Xylariaceae. The modern mycologists are in- 

 clined to reduce the first four to two, thus recognizing only three families. 

 The most extensive recent work on this group is a series of studies by 

 Wehmeyer (1926, 1933) on the life histories of these fungi. He points out 

 that these stromatic forms exhibit a gradual transition from fungi in 

 which the stroma is vague in outline and not very definite in structure to 

 those with a highly organized stroma. In the simplest type of stroma the 

 surface of the substratum is blackened by the coloring of the mycelium. 

 Wehmeyer states: "The next step in stromatic development comes about 

 by the proliferation of the mycelium within the substratum. As this 



