The hyphal mode of growth, i.e.
In Physma, Arnoldia, Phylliscum and other genera the gonidia are killed sooner or later by special hyphal branches, haustoria, which pierce the membrane of the algal cell, penetrate the protoplasm and absorb the contents (fig.
Special short hyphal branches which are in close contact with the membrane of the algal cell (fig.
They arise usually in the gonidial layer of the thallus by division of the gonidia and the development around them of the hyphal investment; their increase in number leads to the rupture of the enclosing cortical layer and the soredia escape from the thallus as a powdery mass (fig.
Xylographa, e, f, Two soredia in the act of germinating; the Graphis, &c.) or hyphal envelope has grown out below into G none (e.g.
Sometimes fatty oil or watery sap is found in swollen hyphal ends, or such tubes contain coloured sap. Cystidia and paraphyses may be also classed here.
Other series of modifications arise in which the tissues corresponding to the stroma invest the sporogenous hyphal ends, and thus enclose the spores, asci, basidia, &c., in a cavity.
Another simple case is where the plane or slightly convex surface of the stroma rises at its margins and overgrows the sporogenous hyphal ends, so that the spores, asci, &c., come to lie in the depression of a cavity - e.g.
In such examples as the above we may regard the hymenium (Solenia, Cyphella), zygospores, or asci as truly invested by later growth, but in the vast majority of cases the processes which result in the enclosure of the spores, asci, &c., in a "fructification" are much more involved, inasmuch as the latter is developed in the interior of hyphal tissues, which are by no means obviously homologous with a stroma.
Thus in Penicillium, Eurotium, Erysiphe, &c., hyphal ends which are the initials of ascogenous branches, are invested by closely packed branches at an early stage of development, and the asci develop inside what has by that time become a complete investment.
The outer parts of the mass then differentiate as a wall or investment, and the interior becomes a hollow, into which hyphal ends grow and abstrict the spores.
Any one of these soon comes to rest on a host-cell, and either pierces it and empties its contents into its cavity, where the further development occurs (Olpidium), or merely sends in delicate protoplasmic filaments (Rhizophydium) or a short hyphal tube of, at most, two or three cells, which acts as a haustorium, the further development taking place outside the cell-wall of the host (Chytridium).
At the same time there are strong grounds for insisting on the resemblances between Endomyces, a hyphal fungus bearing yeast-like asci, and such a form as Saccharomyces anomalus.