=The Button Stage of the Mushroom.=--The "spawn" stage, or strands of mycelium, is the vegetative or growing stage of the mushroom. These strands grow through the substance on which the fungus feeds. When the fruiting stage, or the mushroom, begins there appear small knobs or enlargements on these strands, and these are the beginnings of the button stage, as it is properly called. These knobs or young buttons are well shown in Fig. 3. They begin by the threads of mycelium growing in great numbers out from the side of the cords. These enlarge and elongate and make their way toward the surface of the ground. They are at first very minute and grow from the size of a pinhead to that of a pea, and larger. Now they begin to elongate somewhat and the end enlarges as shown in the larger button in the figure. Here the two main parts of the mushroom are outlined, the stem and the cap. At this stage also the other parts of the mushroom begin to be outlined. The gills appear on the under side of this enlargement at the end of the button, next the stem. They form by the growth of fungus threads downward in radiating lines which correspond in position to the position of the gills. At the same time a veil is formed over the gills by threads which grow from the stem upward to the side of the button, and from the side of the button down toward the stem to meet them. This covers the gills up at an early period. [Illustration: FIGURE 6.--Agaricus campestris. Under view of two plants just after rupture of the veil, fragments of the latter clinging both to margin of the pileus and to stem. (Natural size.)] =From the Button Stage to the Mushroom.=--If we split several of the buttons of different sizes down through the middle, we shall be able to see the position of the gills covered by the veil during their formation. These stages are illustrated in Fig. 4. As the cap grows in size the gills elongate, and the veil becomes broader. But when the plant is nearly grown the veil ceases to grow, and then the expanding cap pulls so strongly on it that it is torn. Figure 5 shows the veil in a stretched condition just before it is ruptured, and in Fig. 6 the veil has just been torn apart. The veil of the common mushroom is very delicate and fragile, as the illustration shows, and when it is ruptured it often breaks irregularly, sometimes portions of it clinging to the margin of the cap and portions clinging to the stem, or all of it may cling to the cap at times; but usually most of it remains clinging for a short while on the stem. Here it forms the annulus or ring. [Illustration: FIGURE 7.--Agaricus campestris. Plant in natural position just after rupture of veil, showing tendency to double annulus on the stem. Portions of the veil also dripping from margin of pileus. (Natural size.)]