VEGETABLE CYTOLOGY 
57 
exogens, and in gall formations. They are soluble in water, alcohol, 
glycerine, and a mixture of alcohol and ether. They are almost 
insoluble in absolute ether and chloroform. They give insoluble 
precipitates with organic bases such as alkaloids and with most of 
the salts of the heavy metals. 
According to their behavior with solution of iron chloride or 
other soluble iron salts two kinds of tannic acid are recognized: (a) 
a form of tannic acid giving a blue color, as that which is found in 
Rhus, Castanea, Granatum, Galla, etc.; ( b ) another tannic acid 
producing a green coloration, as that found in Krameria, Kino, 
Mangrove bark, Quercus, Catechu, etc. 
If sections are placed in a 7 per cent, solution of copper acetate 
for a week or more, then placed on a slide in 0.5 per cent, aqueous 
solution of ferric chloride, and after a while washed with water and 
mounted in glycerin, an insoluble brownish precipitate will be pro- 
duced in those cells containing tannin. 
16. Proteins. — Proteins are complex nitrogenous substances 
forming the most important of the reserve foods of plants. They are 
found in all the living and many of the dead cells of plants although 
most abundant in seeds. Protoplasm, itself, is composed largely 
of these substances. They all contain carbon, hydrogen, oxygen, 
nitrogen and sulphur, and many contain in addition phosphorus. 
They are formed by the addition of nitrogen, sulphur and fre- 
quently phosphorus to elements of grape sugar. The nitrogen, 
sulphur and phosphorous elements are obtained from nitrates, 
sulphates and phosphates which are dissolved in the water taken 
in through the roots. The names of proteins recorded may be 
found by the hundreds. These are grouped into chemical classes, 
the most important of which from the standpoint of their occurrence 
in plants are the globulins, albumens, glulelins, nucleins, and gliadins. 
Of these the globulins are found most extensively. Globulins are 
insoluble in water but soluble in sodium chloride solutions. They 
do not coagulate upon the application of heat. 
Albumens are soluble in water and coagulate with heat. 
Glutelins are insoluble in water, sodium chloride solution and 
st rong alcohol. 
