NON-PROTOPLASMIC CELL CONTENTS 93 
synthesis appears to involve the following steps: (1) the union 
of molecules of dextrose or some other simple sugar to nitrogen 
to form amino acids; (2) the combining of amino acids to form 
polypeptides; (3) the building up of polypeptides into simple 
proteins; (4) the union of phosphorous or sulfur to simple 
proteins to form complex proteins. The names of proteins recorded 
may be found by the hundreds. These are grouped into 
chemical classes, the most important of which from the stand- 
point of their occurrence in plants are the globulins, albumens, 
glutelins, 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 
strong alcohol. 
Gliadins are nearly or wholly insoluble in water but soluble in 
70 to 90 per cent. alcohol. 
Nucleins are insoluble in water but soluble in alkaline 
solutions. 
The following tests are of value in determining the presence of 
proteins: 
Lugol’s solution (made by dissolving 5 Gm. of iodine and 10 Gm. of potassium 
iodide in enough water to make product weigh 100 Gm.) stains proteins yellow or 
brown 
Concentrated nitric acid stains proteins yellow. This color becomes deeper 
upon the addition of ammonia water. ' a 
Milon’s reagent (made by dissolving 3 cc. of mercury in 27 cc. of fuming nitric 
acid without heat and adding an equal volume of distilled water) stains proteins a 
brick-red. : 
Concentrated solution of nickel sulfate colors proteins yellow or blue. 
If sections are placed for an hour or two in a solution of 1 Gm. of sodium 
phospho-molybdate in 90 Gm. of distilled water and 5 Gm. of nitric acid, the 
proteid substances appear as yellowish granules. 
The globulins (phytoglobulins) frequently occur in bodies 
called ‘‘aleurone grains.” 
ALEURONE GRAINS 
Aleurone grains are small bodies found in seeds particularly 
those containing oil, and like starch grains often are characteristic 
