dded that the capillitial threads are
always exceedingly delicate, probably tubular, but never filled with
lime throughout; the peridium may be almost nude or encrusted with lime,
which, where present, is always amorphous, never crystalline; the
sporangia when distinct may be either sessile or stipitate, and the
stipe in the latter case is often hollow and charged with lime. In
capillitium intermediate between _Leocarpus_ and _Badhamia_, since in
the first the capillitium is unequally calcareous, diverse, while in
_Badhamia_ the capillitium is intricate and calcareous throughout.

As first set up by its founder, the genus included diverse forms, only
one or two of which would be included in the genus as now limited.[20]
Persoon, however, was left to develop the matter to suit himself, and in
successive works gave, under this generic name, more and more prominence
to forms now so referred. Fries, _Syst. Myc._, III., pp. 127 _et seq._,
still better establishes the genus, though still including forms that,
judging from the description, seem to belong elsewhere. Twenty years
later Fries revising somewhat his earlier work thought to improve the
chances of future students by reducing the number of physarums. This he
would do by setting out certain evidently inter-related forms to make a
new genus, _Tilmadoche_.

He named two or three species only, leaving his sucessors to add others
as occasion offered.[21]

Rostafinski approved the good intention of Fries, but in the
_Monograph_, he entirely re-cast the genus as constituted by Fries;
actually called the species 'first cited' a typical physarum! Would not
have it in the new genus at all, first or last; but instead took the
second species of Fries as the type and added several forms, some from
the Friesian list, to make up a respectable group.

Until quite recently writers on the subject have generally approved the
course adopted by the Polish author. The arrangement showed features of
convenience, even if artificial to a degree. Perhaps we gain advantage
in all directions if we treat the original genus _Physarum_ as a whole,
but in the key take advantage of Fries' suggestion. We may write--

=Key to the Species of Physarum=

1. Capillitium irregularly reticulate throughout; calcic
nodes various _Physarum_

2. Capillitium more regular, especially below, furcate;
nodes fusoid