In these there is a thallus which starts from a central point and continually divides in a forked or dichotomous manner.

The lichen-thallus is composed of chains or groups of round chlorophyl-containing cells, called "gonidia," and masses of interwoven rows of elongated cells which constitute the hyphæ.

Under certain conditions single cells of the gonidia become surrounded with a dense felt of hyphæ, these accumulate in numbers below the surface of the thallus, until at last they break out, are blown or washed away, and start germination by ordinary cell division, and thus at once reproduce a fresh lichen-thallus.

Under certain conditions single cells of the gonidia become surrounded with a dense felt of hyphæ, these accumulate in numbers below the surface of the thallus, until at last they break out, are blown or washed away, and start germination by ordinary cell division, and thus at once reproduce a fresh lichen-thallus.

They are set free by the rupture of the ascus, and germinate by putting out through their walls one or more filaments which branch and form the thallus of a new individual.