Order 16. Melanconidaceæ.
Order 17. Melogrammataceæ.
Order 18. Xylariaceæ. This order is the most highly developed of the Sphæriales. The stroma arises on the surface of the substratum, which is generally dead or decorticated wood; it is well-developed, crustaceous, hemispherical or upright. In the younger conditions it is covered with a layer of conidia, and later on it bears the perithecia, arranged in a layer immediately beneath its surface. The ascospores are of a dark colour. Often also there are free conidiophores.
Fig. 122.—Xylaria hypoxylon (nat. size) on a tree stump: a younger, b an older stroma, both of which, with the exception of the black lower portion, are covered with white conidia; n, spot where the perithecia are developed; c an old stroma with upper part fallen off; d, e large branched stromata; k conidia.
Hypoxylon and Ustulina have a cushion-like or crustaceous stroma.—Xylaria has a club-shaped or branched stroma, often several centimetres high. X. hypoxylon (Fig. [122]) and X. polymorpha occur on old tree stumps.—Poronia grows on old horse dung, and has a conical stroma.
Sub-Family 3. Dothideales.
The perithecia are always embedded in a black stroma, and are not distinctly separated from it. The accessory forms of reproduction are: conidiophores, conidiocarps, and yeast-like conidia. The majority are parasites. One order.
Order Dothideaceæ. Phyllachora graminis produces scab-like patches on the leaves of the Grasses.—Scirrhia rimosa grows on the leaf-sheathes of Phragmites.—Rhopographus pteridis on Pteridium aquilinum.