43 
wholly unacquainted with the use of the microscope, will seek in- 
structions in some manual specially devoted to the use of this in- 
strument, but it seems desirable to make a f6w general observa- 
tions upon the structure and examination of these plants. 
The sporangia are thin-walled, membranaceous sacs, the walls 
consisting of two layers of cells, the outermost layer translucent, 
but in a few of our species mixed with brown (schlerenchym) cells, 
giving the sporangia a spotted appearance. The velum in all our 
species only partly covering the sporangium is easily seen with 
the naked eye in fresh plants ; in the case of dried specimens it is 
well to soak the whole plant in water previous to examination. 
At the leaf base and just above the sporangium is a small, trian- 
gular, membranaceous organ (ligule) whose function is not well 
understood. It can be seen to good advantage only in fresh leaves 
and is apparently of small diagnostic value. 
The macrospores should be examined when perfectly dry, with 
a power of 50-75 diameters ; and it will be found that if they are 
heated sufficiently to cause them to assume a light brown tint, as 
by holding them on a glass slip over the chimney of an ordinary 
lamp, that the sculpture will become more evident by reason prob- 
ably of a diminution of internal reflections. The microspores are 
very minute bodies, having the appearance of a fine powder when 
removed from the sporangium. They are about one one-thous- 
andth of an inch in length, and in a single sporangium of some 
species are probably contained by millions. They may be exam- 
ined under water or in balsam by transmitted light, and should 
also be viewed by reflected light as opaque objects, with a magni- 
fication of 300-400 diameters. Before any conclusions are drawn 
regarding the condition of the surface of either macrospore or mi- 
crospore, care should be taken that those under examination be 
perfectly mature, as unripe spores have very frequently an appear 
ance differing much from that of those fully developed. This ap- 
plies also to spores from young plants. 
In the preceding descriptions the dimensions of the spores are 
