DEVELOPMENT OF THE MUSHROOM. 7 



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 



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.) 



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. 



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 forma- 

 tion. 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 rup- 



