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.

These contents are now gradually forming themselves into the spore or "gonidium," as Carpenter calls it, in distinction from the true sexual spores, which he terms "oospores."

At the same instant, the inclosed gonidium (for it is now seen to be fully formed) acquires a rotary motion, at first slow, but gradually increasing until it has gained considerable velocity.

The old cell wall seems to offer considerable resistance to the escape of the gonidium, for the latter, which displays remarkable elasticity, is pinched nearly in two while forcing its way through, assuming an hour glass shape when about half out.

The motile force is imparted to the gonidium by dense rows of waving cilia with which it is completely surrounded.

After the gonidium comes gradually to a rest its cilia soon disappear, it becomes perfectly globular in shape, the inclosed granules distribute themselves evenly throughout its interior, and after a few hours it germinates by throwing out one, two, or sometimes three tubular prolongations, which become precisely like the parent filament (Fig 2).

Eminent English authorities have advanced the theory that the ciliated gonidium of Vaucheria is in reality a densely crowded aggregation of biciliated zoospores, similar to those found in many other confervoid algæ.

It is also to be noted as a significant fact, that the cellulose wall was intact at the apex, instead of showing the opening through which in ordinary cases the gonidium escapes.

It would seem to be a reasonable inference, I think, based upon the theory above stated, that in this case the newly formed gonidium, unable to escape from its prison by reason of the abnormal strength of the cell wall, became after a while resolved into its component zoospores.