ORDER MELANCONIALES 



581 



Family Excipulaceae. The pycnidia open out early to form a more 

 or less deep, cup or saucer-shaped structure, tough or hard and black, 

 either arising subepidermally or subcortically and breaking through to 

 the outside, or in some cases external from the first. Largely saprophytic 

 on twigs, stems, etc., less often on leaves. It is sometimes difficult to 

 distinguish certain subcortical species of this family from the following 

 order (Melanconiales). Bender recognizes 59 genera. Excipula and Discula 

 (Hyalosporae) and Discella (Hyalodidymae) are among the genera with 

 the greatest number of species. 



Tehon (1940) separated from among the genera usually included in 

 the Leptostromataceae two families, Pycnothyriaceae and Rhizothyri- 

 aceae, which he combines in a distinct order Pycnothyriales. These differ 

 from the Leptostromataceae in bearing their spores on the under side of 

 the pycnidial cover instead of basally. 



Order Melanconiales. This order of 92 genera^ and over 600 North 

 American species consists of but one family, Melanconiaceae. To a large 

 extent the species are parasitic, causing the type of plant disease known 

 as anthracnose. The three form genera, Gloeosporium (Fig. 193A), Col- 

 letotrichum (Fig. 194A), and Myxosporium (Hyalosporae), contain some 

 of the most destructive parasites of cultivated plants. They differ by 

 arbitrary characters. Colletotrichum produces stiff colorless or colored 

 bristles (setae) around the acervulus while these are lacking in the other 

 two. Gloeosporium occurs on herbaceous host structures while Myxo- 

 sporium occurs on woody stems. How artificial these distinctions are may 

 be seen in the case of the fungus called Colletotrichum gloeosporioides Penz., 

 a common parasite of the leaves, young twigs, and fruits of species of 

 Citrus and many other genera. When inoculated upon the mango (Man- 

 gifera indica L.) setae are produced on some of the acervuli on the twigs 





• r^r 



Fig. 193. Melanconiales, Family Melanconiaceae. (A) Gloesporium populi-albae 

 Desm.; section through acervulus. (B, C) Septogloeum mori (Lev.) Briosi & Cav. 

 (B) Section through acervulus. (C) Spores. (A, after Briosi and Cavara: Fascicle VI, 

 No. 147. B-C, ibid., Fascicle I, No. 21.) 



2 The figures for this and the following orders and families are taken from H. B. 

 Bender (thesis, 1931) 



