ies of development. All those statements on the
sphere of form and connection, which have for their basis such a
superficial work, and are not based on the clear exposition of the
continuity of development, as by the origin of the connection of
the _Mucor_ with _Penicillium_, _Oidium lactis_ and _Mucor_, _Oidium_
and _Penicillium_, are rejected as unfounded.

A source of error, which can also interfere in the last-named
superficial method of cultivation for experiments, is, viz., that
heterogeneous unwished-for spores intrude themselves from without,
among the seed which is sown, but that has been until now quite
disregarded. It is of great importance in practice, but in truth, for
our present purpose, synonymous with what we have already written.
Those learned in the science of this kind of culture lay great stress
on its importance, and many apparatuses have been constructed, called
"purely cultivating machines," for the purpose of destroying the
spores which are contained in the substratum, and preventing the
intrusion of those from without. The mixture in the seed which is sown
has of course not been obviated. These machines may, perhaps, in every
other respect, fulfil their purpose, but they cannot change the form
of the question, and the most ingeniously constructed apparatus cannot
replace the attention and intellect of the observer.[B]

Two distinct kinds of phenomena have been grouped under the term
"polymorphy." In one series two or more forms of fruit occur
consecutively or simultaneously on the same individual, and in the
other two or more forms appear on a different mycelium, on a different
part of the same plant, or on a matrix wholly distinct and different;
in the latter case the connection being attested or suspected
circumstantially, in the former proved by the method suggested by De
Bary. It will at once be conceded that in cases where actual growth
and development substantiate the facts the polymorphy is undoubted,
whilst in the other series it can at best be little more than
suspected. We will endeavour to illustrate both these series by
examples.

One of the first and earliest suspected cases of dualism, which long
puzzled the older mycologists, was observed amongst the Uredines, and
many years ago it was held that there must be some mysterious
association between the "red rust" (_Trichobasis ruligo vera_) of
wheat and grasses and the "corn mildew" (_Puccinia graminis_) which
succeeded it. The s