PROGRESS OF MICROSCOPICAL SCIENCE. 37 
lower surface. This black dust again simply consists of nothing but 
cells, but in this case the cells are termed spores. These latter are 
of a somewhat different nature from-the simple cells of the flesh of 
the mushroom, and their outer coat in this species is changed in 
colour from transparent to purple-black, possibly from contact with 
the air. The cells in the stem of the mushroom are sausage-shaped, 
and grow vertically ; on reaching the cap these cells spread over in 
an umbrella fashion, and descend into the internal substance of each 
individual gill. This internal mass of cells within the gill is termed 
the ‘trama’ by botanists. To understand how the mushroom pro- 
duces its seeds or spores, a slice should be cut off the side of the cap 
of a mushroom from the top downwards. Where the sectional part 
is now exposed, the gills which are cut through will look like so 
many small fine teeth of acomb. With a sharp lancet a very small 
thin transparent fragment must now be sliced off from the top down- 
wards, and placed upon a glass for examination under the microscope. 
When magnified 250 diameters this fragment will be seen to consist 
wholly of simple cells. These ‘trama’ cells are of some importance, 
because certain members of the mushroom tribe have no larger cells 
of this nature. As these latter cells gradually grow to the exposed 
surface on each side of the gill, they get considerably smaller in size, 
denser, and less and less transparent. The exposed surface of the gill 
is the fruiting, spore-bearing, or hymenial surface. The spores in all 
the mushroom tribe are produced in clusters of four on each basidium, 
but on the common mushroom and all its varieties, as far as I have 
seen, these four spores are generally produced two at a time, and as 
the first two drop off the last two appear, so that it is seldom that 
more than two are seen in situ at the same time. This phenomenon 
teaches a valuable lesson, and one which has, as I conceive, been 
quite erroneously interpreted by Professor Sachs,* who says the 
common mushroom only produces two spores on each basidium, 
and so illustrates the subject in his fig. 174. The cells of the 
mushroom increase in number by apical growth. The last-formed 
cell repeats the process continuously till the fungus is complete and 
the special cells (spores) destined for the reproduction of the species 
are reached. The basidium is first a simple cell, seen in two posi- 
tions. This simple cell becomes potentially (but often indefinitely) 
divided by a longitudinal partition ; each of these divided portions 
produces a branch, and each of these branches bears a spore, which in 
its turn is again cut off by cell division, this time transversely. The 
basidium is now again longitudinally divided ; these portions in their 
turn also produce new branches, which give rise to two more spores, 
each spore again cut off by a transverse septum. As the two last- 
formed spores increase in size they gradually push the two old ones 
off their supports, so that unless the whole process is very carefully 
watched it might be concluded that the mushroom produces only two 
spores (instead of four) on each basidium, as stated by Professor 
Sachs. 
“'The mature spores on germination of course reproduce the species 
* «HWandbook,’ p. 251. 
