Starch-grains are altered by boiling in water, becoming swollen and often changed into curious forms, the rings becoming faint or disappearing. If a piece of boiled potato be examined, the starch-granules will seem to have vanished from the cells, which are swollen and covered with an irregular kind of network. The network consists of parts of the protoplasm situated in the interstices of the starch-granules, and solidified or coagulated by the heat. On crushing the cells by pressing upon the cover, the starch-granules will escape, swollen and partly fused together; but they may easily be recognized as consisting of starch by the iodine test. The granules of “tous les mois” starch are particularly well adapted for showing the concentric rings, the granules being about twice as large as those of the potato. Starch-granules are best examined in water; and a small quantity only of the starch must be placed on the slide, if the structure of the granules is to be seen clearly. They may be mounted in glycerine, although this makes them very transparent. To those who possess a polariscope, starch-granules are particularly interesting, as they exhibit a black cross, and, with a plate of selenite laid beneath the slide, a beautiful play of colours. In addition to the starch and chlorophyll, the cells of plants contain other matters, as gum, sugar, &c.; but as they are dissolved in the cell-liquid, they are not visible. In the cells of certain plants, however, spherical globules, with light centres and black outlines, will be met with: these consist of oil. _Raph´ides._--Lastly, occurring in the cells of plants, especially such as are soft and juicy (succulent), will be found minute, hard, colourless crystals, called _raphides_ (ῥαφὶς, a needle). These are most frequently needle-like or acicular (_acus_, a needle), but sometimes prismatic or rod-like with flat sides; they are also not unfrequently grouped into little tufts. They may be readily found in a piece of the stem of garden-rhubarb (Pl. I. fig. 5 _a_), or of the common balsam. _Porous and spiral cells._--The walls of the cells of cellular tissue are sometimes covered with little dots (Pl. I. fig. 11 _a_), or slit-like markings; the cells are then called porous cells. A specimen of them may be obtained from a section of the pith of the elder (_Sambúcus nígra_). Sometimes cells exhibit the appearance of a spiral line marking their walls, as if a little bell-spring were coiled up in them (Pl. III. fig. 2 _a_). These are called spiral cells, or spiral fibrous cells, and the tissue formed by them is called fibro-cellular tissue. We now leave the cells of ordinary cellular tissue, to examine those in which the dimension of length predominates, so that they form tubular cells; and first of those required to possess strength and firmness, combined with flexibility. These qualities are met with in the cells constituting