Another interesting object to the young microscopist is afforded by the spores of the equiseta (or horsetails, as they are often called). These may be obtained by shaking the higher portion of the stems when the spores are ripe. They will then fall like small dust, and may be placed under the microscope. The spores are then seen to consist of a somewhat heart-shaped mass with bands rather intricately curled around it. As they dry these bands expand, and are seen to be four lines at right angles, with the ends clubbed, as it may be called. If, whilst watching them, the spores are breathed upon, these bands immediately return to their former state, and are closely curled around the spore; but as they gradually dry again expand. This experiment may be repeated many times, and is a very interesting one. The above are the principal objects which could not possibly be included in any of the former chapters, but would have left a most interesting branch untouched had it been neglected. There is another subject also which should not be passed by--viz., the production of minute pictures which serve as objects for microscopic examination. I may here mention that as this manual is simply to enable the young student to prepare and mount his objects, the photography of _magnified_ objects has evidently no place here. Few slides caused so much astonishment as these minute photographs when first exhibited; small spots were seen to contain large pictures, and a page of printed matter was compressed into the one-hundredth part of a square inch. It would be impossible in this place to give the inquirer any instruction in the manipulation of photography, so it must be assumed that he already knows this. We will first consider the process performed by artificial light. The collodion employed in photographing generally shows as much structure when magnified as is found in linen of moderate texture; but this is not always the case, as some samples bear much enlargement without any of this appearance. It is evident that a structure so coarse would make it entirely unfit for these minute pictures, as all the small markings would be destroyed, or so interfered with that no great enlargement would be practicable. To obtain almost structureless collodion is not an easy matter, and a clever practitioner in this branch of photography states that he knows of no method to accomplish this with certainty, but he himself tries different samples until he falls upon a suitable one, which he then lays aside for this object. A beneficial effect is often derived from keeping the collodion awhile, but this is not always the case. The slides should be chosen of an equal thickness, so that when focussed upon one no re-adjustment may be necessary for the others. The glass should, of course, be free from any roughness, scratches, or other imperfections, and of first-rate quality and colour.