40 MISSOURI BOTANICAL GARDEN. 
of humus increasing in width (c). In drying, numerous 
fissures have appeared in the mass. The lignin layer be- 
comes narrower and narrower, then disappears and at last 
even the primary lamella no longer gives the lignin reaction, 
and the whole is transformed into humus compound (e). 
The positions of the original cells are still very evident, 
and here and there a piece (u) of unchanged cell-wall re- 
mains in the homogeneous mass of matter. 
The action of the rotted membranes on polarized light 
has already been mentioned. The primary lamella shows 
decided light lines in a transection of the kind shown on 
Pl. 3, fig. 2, but as soon as the wood no longer gives the 
lignin reaction it appears dark when the Nicol prisms are 
crossed. The same is true of the humus compound. 
Whatever the change is which changes a non-homogeneous 
body to a homogeneous one, it is one which takes place 
when the chemical structure of the non-homogeneous body 
begins to change. When a portion of the humus mass is 
dissolved in dilute KOH there appear in the center of this 
mass certain highly refractive bodies }-14 mw in diameter, 
of very definite structure resembling human blood corpus- 
cles somewhat (Pl. 5, fig. 8). They are hexagonal in 
shape with blunted corners and have a much depressed 
center, so that the edge view shows four contour lines, two 
parallel lines, and two of an hour-glass shape. When exam- 
ined with polarized light they shine brightly when viewed 
from the edge, and as they have a decided Brownian 
motion, they alternately flash and disappear. Their very 
variable size, but constant form, as well as their appearance 
in polarized light, suggest that they are crystals of some 
sort. Hartig* says that the comparatively high resistance 
of the walls bounding the lens-shaped pits, is probably due 
to the large number of calcium oxalate crystals imbedded in 
these walls; he indicates these by fine dots (fig. 13). The 
* Hartig, R. Der achte Hausschwamm 57 
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