hia clavata_ and _H. vesparium_ are often side by side
on the same substratum, but do not mix, and their perfected fruits
presently stand erect side by side, each with its own characteristics,
entirely unaffected by the presence of the other. On the other hand, it
is probable that some of the forms which, judged by their different
fructifications, and by this alone, are to us distinct, may be more
closely related than we suspect, and puzzling phases which show the
distinctive marks supposed to characterize different species are no
doubt sometimes to be explained on the theory of plasmodial crossing;
they are hybrids.

Under certain conditions, low temperature, lack of moisture, the
plasmodium may pass into a resting phase, when it masses itself in heaps
and may become quite dry in lumps of considerable size, and so await the
return of favorable conditions when former activity is quickly resumed.
Sometimes the larger plasmodia pass into the resting phase by undergoing
a very peculiar change of structure. In ordinary circumstances the
abundant free nuclei demonstrable in the plasmodium afford the only
evidence of cellular organization. In passing now into the condition of
rest, the whole protoplasmic mass separates simultaneously into numerous
definite polyhedral or parenchymatous cells, each with a well-developed
_cellulose wall_.[4] When the conditions essential to activity are
restored, the walls disappear, the cellulose is resorbed, and the
plasmodium resumes its usual habit and structure.

The plasmodial phase of the slime-mould, like the hyphal phase of the
fungus, may continue a long time; for months, possibly for years. The
reason for making the latter statement will presently appear. But
however long or short the plasmodial phase continue, the time of fruit,
the reproductive phase, at length arrives. When this time comes, induced
partly by a certain maturity in the organism itself, partly no doubt by
the trend of external conditions, the plasmodium no longer as before
evades the light, but pushes to the surface, and appears usually in some
elevated or exposed position, the upper side of the log, the top of the
stump, the upper surface of its habitat, whatever that may be; or even
leaves its nutrient base entirely and finds lodging on some neighboring
object. In such emergency the stems and leaves of flowering plants are
often made to serve, and even fruits and flowers afford convenient
resting places. The object