436 



white, in others they are pink, in others some shade of yellow or rust- 

 color, in others purple-brown, and in still others they are black. A 

 single spore of any mushroom is too small to be seen with the naked 

 eye, but when a sufficient mass of them is obtained the color can readily 

 be recognized. If the stem is removed from a fresh mushroom and 

 the cap is placed, gills down, on a sheet of paper and covered with 

 an inverted tumbler the spores will fall to the paper in great numbers, 

 and within an hour or so an impression of the gill surface, consisting 

 entirely of spores, will be formed on the paper. Such an impression 

 is called a spore print (Fig. 2). One of the first things to do, then, 

 when the genus of a species is in doubt, is to make a spore print to 

 determine the color of the spores. 



Fig. 2. Spore print of Collyhia radicata. 



, ' Use of the Key 



In the key to the gill fungi on page 437 the genera are arranged in 

 columns according to the spore color, and in the first column some 

 other differences between genera are tabulated. Suppose now that on 

 our first collecting trip we find a cluster of orange-colored mushrooms. 

 We probably have seen the same kind before but we do not know its 

 name. We at once cut the stem from one specimen and place the cap, 

 gills down, on a piece of white paper and invert a tumbler over it. If we 

 can spare another specimen we arrange it in the same way on a piece 

 of black paper. Then with a specimen in hand, we turn to the key. 

 At the beginning of the kev we find, "I. Flesh vesiculose". and three 



