122 PLANT ANATOMY. 
saliva acts upon the latter substance, dissolving it, and leaving 
a frame-work or skeleton of cellulose behind. 
On the other hand it is to be remembered, as one of us has 
shown,’ that the “ granulose” has lost all the characters of 
starch. Furthermore, the acceptance of cellulose in the residue 
is based upon its solubility in ammoniacal solution of oxide of 
copper, the loss of its property of swelling in hot water, and the 
non-appearance of any coloration by treatment with iodine. But, 
on the one hand, amylum is itself soluble to a slight degree in 
ammoniacal oxide of copper, and, on the other hand, ‘‘ granu- 
lose” is just as little colored by iodine as the here accepted 
cellulose, while the swelling property of starch may also be 
destroyed by boiling with glycerin and water. There are thus 
not sufficient reasons presented for concurring in Nigeli’s pro- 
position. 
Starch containing water, but not that which has been deprived 
of the latter, possesses a highly remarkable attractive power for 
iodine. It is capable of so combining with it, that the granule, 
the mucilage, or the solution of starch thereby assume colora- 
tions which correspond to those peculiar to iodine itself in its 
different conditions of aggregation and in its solutions. The 
blue, violet, or reddish color which amylum presents when it is 
brought in contact with iodine was first observed by Colin and 
Gaultier de Clanbry* in March, 1814; the other shadings in 
violet, red, reddish-yellow, yellow, and brown were studied in 
1863, and later by C. Niigeli with great thoroughness. These 
shadings of color are limited by the varying reciprocal relations 
in the amounts of iodine and starch, as also by the presence of 
hydriodic acid and other substances. 
Slight amounts of very small starch granules as in chlorophyll 
(page 102) may be made more distinctly visible by causing them 
to swell by means of caustic alkali, subsequently washing the 
fe cea “ Starke und Cellulose,” in Archiv der Pharm, 196 (1871), 
** Annales de Chimie ” 90, p. 93. —Stromeyer, at Géttingen, in Decem- 
ber, 1814, pointed out the delicacy of this reaction in Gilbert’s‘* Annalen 
der Physik,” 49, p. 147, 
