For the study of the life history of a Fern one cannot do better than take the commonest of our native species, the Male Fern (_Nephrodium filix-mas_). Seeing that the general aspects of the plant are fully described in a later chapter, there is no need to enter into such matters at the present moment. We may, however, examine a fertile leaf of the Fern in order that we may start at the beginning of a really interesting romance. A very small magnification of the brown patches on the back of the frond, which we remember are called sori, will reveal their true character. After removing the kidney-shaped cover (indusium) we shall be able to see the spore cases or sporangia quite clearly. Each of these consists of a capsule borne on the end of a stalk. These sporangia are seen to grow out from the sides of a mass of special tissue, known as the placenta, from which the indusium really arises. On occasions a curious club-shaped hair which secretes resin can be observed on the stalks of the sporangia. There seems to be no satisfactory explanation as to the part which this process plays. The capsule of the sporangium is much flattened, and has not been inaptly compared to a watch-case. Its wall is very thin, being composed of a single layer of cells. Around the edges of the little case there is a row of large and thickened cells which form the ring or annulus. Here it may be mentioned again that the structure of this annulus varies greatly in the different families, and is often a useful distinguishing feature. To return to our Male Fern, the annulus is plainly seen to start from the stalk of the sporangium at one side of the capsule, and it can be traced right over the top to a situation about half-way down on the other side. The chief business of the annulus is to bring about the opening of the sporangium in such a way that the spores are violently expelled. This happens in the following manner. When the contents of the sporangium are mature the wall of the capsule, and especially the cells forming the annulus, begin to lose water. The sides of the capsule start to draw inwards, and ultimately the annulus suddenly straightens out and the sporangium is torn open, the actual rupture taking place just at the base of the ring.