162 VEGETABLE PHYSIOLOGY 
but they are decomposed during the process. Their 
solutions have generally a power of deflecting a ray of 
polarised light to the left. 
The best known groups into which proteins have been 
divided are the following :— 
1. Ausumins.—These are soluble in distilled water, and 
if the solution is heated, the protein is converted into a 
peculiarly insoluble form, known as coagulated protein, and 
deposited as a granular or flocculent precipitate. As the 
temperature rises the liquid becomes markedly opalescent 
before the separation of the protein. The change takes 
place at a point which lies between 65° and 80° C., its 
exact place depending upon the nature of the albumin and 
the reaction and concentration of the protein solution, 
This point is known as the coagulation temperature. 
Albumins can be precipitated unchanged by saturating 
their solutions with sodio-magnesic sulphate. They are 
not of frequent occurrence in plants, but can be extracted 
from certain roots. 
2. GuropuLtins.—These differ from albumins in not 
being soluble in ‘distilled water. They can be dissolved by 
adding a little neutral salt, such as sodium chloride. Their 
solutions are coagulated on heating, but they show a con- 
siderable variability as to the coagulation temperature, 
which in the case of some is as low as 55° C. Most of 
them, however, remain unchanged below 75°-80° C. They 
can be precipitated by saturating their solutions with 
magnesium sulphate. If sodium chloride igs used instead 
of the latter, an incomplete precipitation usually takes 
place. , Different members of the group show different 
degrees of solubility in solutions of sodium chloride; some 
require only a trace of the salt ; others need 8-10 per cent.; 
and a few are soluble only in saturated solutions.) 
The proteins found in plants belong chiefly to this 
class. Globulins can be readily extracted from most seeds, 
and probably this form of protein is the one which occurs 
in the green parts of plants. 
