Few persons would suppose that the slug-like object on Fig. 3, the little rounded globules with a pair of hair-like appendages, and the round disc with a dark centre, are only different forms of the same organism. Such, however, is the case, and these are three of the modifications which the Protococcus undergoes. This vegetable may be seen floating like green froth on the surface of rain-water. On collecting some of this froth and putting it under the microscope, it is seen to consist of a vast number of little green bodies, moving briskly about in all directions, and guiding their course with such apparent exercise of volition that they might very readily be taken for animals. It may be noticed that the colour of the plant is sometimes red, and in that state it has been called the Hæmatococcus. The “still” state of this plant is shown in the round disc. After a while the interior substance splits into two portions; these again subdivide, and the process is repeated until sixteen or thirty-two cells become developed out of the single parent-cell. These little ones then escape, and, being furnished with two long “cilia” or thread-like appendages, whirl themselves merrily through the water. When they have spent some time in this state, growing all the while, they lose their cilia, become clothed with a strong envelope, and pass into the still stage from which they had previously emerged. This curious process is repeated in endless succession, and causes a very rapid growth of the plant. The moving bodies are technically called zoospores, or living spores, and are found in many other plants besides those of the lowest order. IV. FIG. 1. Gory Dew, Palmella cruenta 2. Palmoglæa macrococca 3. Protococcus pluvialis, _a_, in its motile, _b_, in its fixed state, _c_, zoospores 4. Closterium 5. Ditto, end more magnified 6. Pediastrum 7. Scenedesmus 8. Oscillatoria 9. Spirogyra 10. Tyndaridea 11. Do. spore 12. Sphærozosma 13. Chlorococcus 14. Scenedesmus 15. Pediastrum, to show cells 16. Ankistrodesmus 17. Cosmarium 18. Desmidium 19. Cosmarium, formation of Resting Spore 20. Cocconema lanceolatum 21. Diatoma vulgare Do. larger frustules, at the side 22. Volvox globator Do. single green body, above 23. Synedra 24. Gomphonema acuminatum Do. larger frustules, below 25. Yeast 26. Sarcina ventriculi 27. Eunotia diadema 28. Melosira varians Do. two bleached frustules 29. Cocconeis pediculus 30. Achnanthes exilis 31. Navicula amphisbœna 32. Uredo, “Red-rust” of corn 33. Puccinea, Mildew of corn 34. Botrytis, mould on grapes Do. Sporules, beside it 35. Do. parasitica, Potato blight 36. Ectocarpus siliculosus 37. Ulva latissima 38. Polypodium Do. single spore, below 39. Moss capsule, Hypnum 40. Mare’s tail, Equisetum, _a_ Do. do. _b_ and _c_ 41. Porphyra laciniata [Illustration: IV.]