144 ~ Brown: Woops FOR MICROSCOPIC STUDY 
thin outer ligno-cellulose layer usually present (Fic. 4, A). 
Fibers in which the mucilaginous layers remain in contact with 
the outer layers on drying ordinarily show large shrinkage checks 
extending radially outward from the center, through the muci- 
laginous portion. Dehydration may be completed by placing 
the slide upon the water bath for a few seconds. In stained 
sections mounted in balsam or dammar, mucilaginous membranes 
are usually shown in the contracted state. In glycerine, water, 
or other media in which the tissue has been mounted without 
dehydration, the mucilaginous layers appear in the swollen con- 
dition. Abbé camera outline sketches of single fibers before and 
after dehydration, made with high power and extended draw tube 
to obtain the greatest possible enlargement, accurately show the 
amount of shrinkage as in Fic. 4, A and B. The mucilaginous 
core of such fibers often contracts over 25 per cent of both radial 
and tangential dimensions on drying, and swells rapidly to original 
size on admission of water. The outer ligno-cellulose layer and 
the middle lamella (M) which is here indistinguishable from the 
primary thickening of the fiber, on the other hand, show relatively 
little change in dimensions. The shrinking and swelling of the 
mucilaginous thickenings is partly independent of the other parts 
of the tissue, so that, as in the case of the Hawaiian woods ex- 
amined by the writer, the wood tissue itself was not observed to 
swell or shrink in proportion to that of the mucilaginous layers of 
the fibers. However, blocks of wood in which mucilaginous fibers 
were abundant, as, for example, Xylosma, were found to shrink 
as much as I2 per cent tangentially and 7 per cent radially on 
drying from saturation. 
6. Reaction to stain and other reagents.—Stains and chemical 
reagents react differently according to the age of the tissue; also, 
after material has been softened in hydrofluoric acid, neither 
stains nor chemical reagents give characteristic reactions. 
In old tissue (heartwood), haematoxylin, Bismarck brown, 
and anilin blue stain the mucilaginous layers with varying in- 
tensity as a substance of variable composition. Very commonly 
stains, particularly the safranin, are readily extracted by the al- 
cohol washes or other treatments in the staining process, so that 
the mucilaginous layers appear slightly or not at all stained in the 
