f it does exist, it must
be extremely defective.

1. SPUMARIA ALBA, Bull. Plasmodium white, amplectant. AEthalium variable
in form and size, resting upon a white, membranaceous hypothallus, and
usually covered by a white, friable, common cortex composed of minute
crystals of lime. The component sporangia elongated, irregular, more or
less branched, the branches rude, deformed, compressed, laterally
confluent, obtuse or pointed at the apex; the walls of the sporangia
thin and delicate, rugulose, pellucid, with a tinge of violet,
iridescent when divested of the crystals of lime. Capillitium of slender
threads, more or less branched and combined into a net; the threads dark
colored, with pellucid extremities, and furnished with occasional rings
or roundish swellings throughout their length. Spores globose, densely
spinulose, dark violaceous, 10-14 mic. in diameter. Plate XII, Fig. 43.

Climbing up and surrounding the stems of small shrubs, herbaceous
plants, culms of grasses, etc., especially those of living plants,
rarely effused upon old wood, bark, leaves, etc. The aethalium from two
or three to several centimeters in length, and with a radial thickness
of two or three to several millimeters. The following forms or varieties
have been distinguished as species at different times:

Var. 1. DIDYMIUM. Sporangia irregular, simple or lobed and branched,
lifted up on narrow, flat extensions of the hypothallus, as if furnished
with short white stipes; the common cortex wanting. This is _Didymium
spumarioides_, Fr.; it is probably a dwarf form of the next variety.
Plate XII, Fig. 42.

Var. 2. CORNUTA. AEthalium large and rugged in outline, cinerous from the
scanty cortex; the sporangia loosely compacted, the branches running
out into numerous free-pointed extremities. Capillitium of rather thick
threads, forming a dense net, with broad expansions at the angles.
Spores 11-14 mic. in diameter. This is _Spumaria cornuta_, Schum. It is
evidently the form so elaborately figured by Rostafinski, and which
Fries says abounds in Northern Europe.

Var. 3. MUCILAGO. AEthalium large, even and uniform in outline, covered
by a thick, white, common cortex; the sporangia laterally confluent and
densely compacted together throughout. Capillitium of rather slender
threads, forming a loose net, scarcely expanded at the angles. Spores
10-13 mic. in diameter. This is _Spumaria mucilago_, Nees, as figured by
Greville in the Scottish Cryptogamic