142 Brown: WooDs FOR MICROSCOPIC STUDY 
of distilled water. Cellulose tissues turn deep blue as soon as 
transferred to 10 per cent hydrochloric acid. If mounted in 
glycerine (acidulated by adding one drop of strong hydrochloric 
acid to 10 c.c. of glycerine) and well cemented with Brunswick 
black or gold size, the blue color will remain several months without 
fading. 
B. CELLULOSE-LIGNIN 
The above test for cellulose may be varied by transfercing the 
section for a brief period to a strong aqueous solution of anilin 
chloride immediately after the treatment with Congo red, the 
remainder of the treatment being the same. Lignified tissues 
appear yellow; cellulose, blue. 
Cc. GUMS 
Gummy substances, both those which are soluble in water and 
those which swell without going into solution (mucilages), are 
constantly met with in woody tissues, occurring in the lumina of 
vessels, tracheids, and other cells, or in intercellular canals or 
cavities, these latter resembling resin cavities. Certain forms 
of each (gums and mucilages) are believed to play the 
r6le of reserve material (Haas and Hill, ’13, p. 125; Griiss, ’96). 
Fibers, composed in large part of mucilaginous inner layers, are 
also of frequent occurrence. The gummy nature of amorphous 
bodies observed in permanent mounts is usually indicated by 
shrinkage checks or other evidences of contraction on dehydration, 
as in Fic. 5 (see further below). Gums may be further distin- 
guished from resins by their insolubility in chloroform. 
Mucilaginous laminae in fibers (‘‘gallertartige Verdickung”’ 
Sanio, 63, p. 105; Solereder, ’08, p. 1143: ‘ Hemicellulose,” 
Griiss, ’96; Schellenberg, ’05: ‘‘ cellulose,” Potter, ’o4: ‘‘mu- 
cilaginous fibers,” Sachs, '75, pp. 35-36; Jeffrey, ’17).—Fre- 
quently woody fibers, particularly of xerophytic species, are 
composed of one or more clear, gelatin-like concentric inner 
layers which shrink greatly on drying (Fic. 4); in young tissue, 
they turn deep violet with zinc chlor-iodide. Solereder ('08, 
p. 1143) records twenty-two families in which such fibers occur, 
and his list is not complete. In a given wood, fibers of this 
description may occur either sporadically or in regular distribution ; 
