is, _Syst. Myc._, III., p. 164. Rostafinski, _Versuch_, p. 5,
_Mon._, p. 229, first correctly limits the genus and separates it from
_Cribraria_. 1873-75.

A single species is widely distributed throughout the world,--

1. DICTYDIUM CANCELLATUM (_Batsch_) _Macbr._

PLATE I., Figs. 6, 6 _a_ and PLATE XIX., Figs. 1, 1 _a_, 1 _b_, 1 _c_,
2, 3.

1789. _Mucor cancellatus_ Batsch, _Elench. Fung._, II., p. 131.
1797. _Dictydium umbilicatum_ Schrad., _Nov. Gen. Pl._, p. 11.
1801. _Cribraria cernua_ Pers., _Syn._, p. 189.
1816. _Dictydium cernuum_ Nees, _Syst. d. Pilz._, p. 117.
1875. _Dictydium cernuum_ (Pers.) Rost., _Mon._, p. 229.
1893. _Dictydium longipes_ Morg., _Cin. Soc. Jour._, p. 17, in part.

Sporangia gregarious, depressed globose, nodding, the apex at length
umbilicate, stipitate, in color brown, or brownish purple; the stipe
varying much in length from two to ten times the diameter of the
sporangium, attaining 5-6 mm., generally erect, more or less twisted and
pallid at the apex, below dark brown, with hypothallus small or none;
calyculus often wanting, when present a mere film connecting the ribs of
the net; the net made up chiefly of meridional ribs connected at
intervals by transverse parallel threads, above an open _Cribraria_-like
network closing the apex and more or less rudimentary; the spores
varying in color through all shades of brown and purple when seen in
mass, by transmitted light reddish, 5-7 mu, smooth or nearly so.

This species in the United States is one of the most variable in the
whole group. The extremes of such variation might easily constitute
types for several distinct species were it not that in all directions
the varieties shade into each other so completely as to defy definition.
We have before us specimens purple throughout and short-stemmed; purple
with stem long, pale and twisted at apex; brown, with the same
variations; short-stemmed, with the apex of the stem pallid, and
long-stemmed, with and without the same peculiarity. Morgan (_Cin. Soc.
Nat. Hist. Jour._, 1893) would set off the purple, long-stemmed forms as
_D. longipes_, "stipe three to five times the sporangium," but here are
forms in which the stem is ten times the diameter of the sporangium,
which yet possess in all other particulars the characters of the
short-stemmed forms. European forms also vary. Massee figures one type;
Lister, one or two others; Rostafinski's figure indicates a taller form;
Fri