[Illustration: FIG. 5.--_A_, a portion of a slime mould growing on a bit of rotten wood, × 3. _B_, outline of a part of the same, × 25. _C_, a small portion showing the densely granular character of the protoplasm, × 150. _D_, a group of spore cases of a slime mould (_Trichia_), of about the natural size. _E_, two spore cases, × 5. The one at the right has begun to open. _F_, a thread (capillitium) and spores of _Trichia_, × 50. _G_, spores. _H_, end of the thread, × 300. _I_, zoöspores of _Trichia_, × 300. i, ciliated form; ii, amœboid forms. _n_, nucleus. _v_, contractile vacuole. _J_, _K_, sporangia of two common slime moulds. _J_, _Stemonitis_, × 2. _K_, _Arcyria_, × 4.] Other protophytes, while evidently enough of vegetable nature, are nevertheless very different in some respects from the higher plants. The protophytes may be divided into three classes: I. The slime moulds (_Myxomycetes_); II. The Schizophytes; III. The green monads (_Volvocineæ_). CLASS I.--THE SLIME MOULDS. 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 (Fig. 5, _A_), 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 filled 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 amœba. 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