"Structural and Systematic Botany", by Douglas Houghton Campbell, PhD., Published by Ginn & Company, 1890.
The Slime Moulds
(pages 12-13)
These curious organisms are among the most puzzling forms with which the botanist has to do, as they are so much like some of the lowest forms of animal life as to be scarcely distinguishable from them, and indeed they are sometimes regarded as animals rather than plants. At certain stages they consist of naked masses of protoplasm of very considerable size, not infrequently several centimetres in diameter. These are met with on decaying logs in damp woods, on rotting leaves, and other decaying vegetable matter. The commonest ones are bright yellow or whitish, and form soft, slimy coverings over the substratum, penetrating into its crevices and showing sensitiveness toward light.
The plasmodium, as the mass of protoplasm is called, may be made to creep upon a slide in the following way: A tumbler is rilled with water and placed in a saucer filled with sand. A strip of blotting paper about the width of the slide is now placed with one end in the water, the other hanging over the edge of the glass and against one side of a slide, which is thus held upright, but must not be allowed to touch the side of the tumbler.
The strip of blotting paper sucks up the water, which flows slowly down the surface of the slide in contact with the blotting paper. If now a bit of the substance upon which the plasmodium is growing is placed against the bottom of the slide on the side where the stream of water is, the protoplasm will creep up against the current of water and spread over the slide, forming delicate threads in which most active streaming movements of the central granular protoplasm may be seen under the microscope, and the ends of the branches may be seen to push forward much as we saw in the amoeba.
In order that the experiment may be successful, the whole apparatus should be carefully protected from the light, and allowed to stand for several hours. This power of movement, as well as the power to take in solid food, are eminently animal characteristics, though the former is common to many plants as well.
After a longer or shorter time the mass of protoplasm contracts and gathers into little heaps, each of which develops into a structure that has no resemblance to any animal, but would be at once placed with plants. In one common form (Trichia) these are round or pear-shaped bodies of a yellow color, and about as big as a pin head, occurring in groups on rotten logs in damp woods. Others are stalked (Arcyria, /Stemonitis), and of various colors, red, brown, etc. The outer part of the structure is a more or less firm wall, which breaks when ripe, discharging a powdery mass, mixed in most forms with very fine fibres.