THE LEAVES 55 



Now make a careful examination of the blades of 

 the leaves you have brought together. Trace the 

 exact outlines on a piece of paper. Are the margins 

 cut to the same pattern ? Compare the upper and 

 lower sides of the leaves. The upper side is fairly 

 smooth and even, while the lower is rougher and 

 shows numbers of ridges or nerves, which may be 

 seen only faintly on the upper side. Fill out the 

 outline of each leaf with a tracing of the nerves. It 

 will be found that the nerves start from the base of 

 the leaf or from a median midrib and divide and 

 subdivide, running to all parts of the blade. The 

 space between the nerves is filled by a soft green 

 tissue, the mesophyl, and the nerves serve as a 

 framework to hold it in position. By searching 

 among the beds of dead leaves in the woods old 

 specimens may be found from which the mesophyl 

 has decayed, leaving the network of the nerves 

 almost entire. The lower surface of the leaf is fur- 

 nished with thousands of minute openings, the 

 stomata. These are usually so small that they may 

 not be seen even with a hand lens ; but if some of the 

 flattish fronds of the liverwort (Conocephalus) can 

 be found, they may be seen on the upper surface 

 with the naked eye. 



