POLYMORPHISM. 183 
it by chance, that the pip of an apple is a product of the develop- 
ment of the apple, and that from the pip an apple-tree can at last 
be developed, that therewith all these bodies are members of a 
sphere of development or form. It is the same with every simi- 
lar experience of our daily life, that where an apple-tree stands, 
many apples lie on the ground, or that in the place where apple- 
pips are sown seedlings, little apple-trees, grow out of the 
ground, is not important to our view of the course of develop- 
ment. Every one recognizes that in his daily life, because he 
laughs at a person who thinks a plum which lies under an apple- 
tree has grown on it, or that the weeds which appear among the 
apple seedlings come from apple-pips. If the apple-tree with 
its fruit and seed were microscopically small, it would not make 
the difference of a hair’s breadth in the form of the question or 
the method of answering it, as the size of the object can 
be of no importance to the latter, and the questions which apply 
to microscopical fungi are to be treated in the same manner. 
If it then be asserted that two or several forms belong to a series 
of development of one kind, it can only be based on the fact of 
their organic continuity. The proof is more difficult than in large 
plants, partly because of the delicacy, minuteness, and fragility 
of the single parts, particularly the greater part of the mycelia, 
partly because of the resemblance of the latter in different 
species, and therefore follows the danger of confusing them with 
‘different kinds, and finally, partly in consequence of the presence 
of different kinds in the same substratum, and therefore the 
mixture not only of different sorts of mycelia, but also that 
different kinds of spores are sown. With some care and pa- 
tience, these difficulties are in no way insurmountable, and they 
must at any rate be overcome; the organic continuity or non- 
continuity must be cleared up, unless the question respecting the 
course of development, and the series of forms of special kinds, 
be laid on one side as insolvable. 
Simple and intelligible as these principles are, they have not 
always been acted upon, but partly neglected, partly expressly 
rejected, not because they were considered false, but because the 
difficulties of their application were looked upon as insurmount- 
