| Popis: |
The very abundant mycelium consists of numerous slender, white or colorless, septate threads, that branch widely, and extend over the leaf in every direction, frequently crossing and interlacing. These threads are usually pressed close to the host, but they do not themselves enter it. They send out at intervals, however, short special branches called haustoria, that penetrate the epidermal cells, serving for the secure attachment of the fungus, and probably also for its nourishment. These haustoria present several forms, and they are of some importance in the classification of the species. In some cases the haustorium simply consists of a slender tube which penetrates the epidermal cell of the host, within which it swells to an oval or club-shaped sac, filled with granular protoplasm. More often there is an external appendage or sucker, that is pressed close to the surface of the epidermal cell; and from this, or from near it on the mycelial thread, the haustorium proper takes its rise and penetrates the epidermis. This external appendage may be smooth and entire, merely constituting a hemispherical swelling on the mycelial thread; or, it may take the form of a flattened disk with an indented margin. In the latter case they are said to be "lobed," in the former, "not lobed." |
