of European chestnut.

Tuberin, " potato tubers.

And, crystalline globulins found in the seeds of flax, squash, castor-bean,
sesame, cotton, sunflower, radish, rape, mustard, and in cocoanuts,
candlenuts, and peanuts.

1C. _Glutelins_

Glutenin, found in the seeds of wheat.

Oryzenin, " " rice.

1D. _Prolamins_

Gliadin, found in the seeds of rye, wheat, with glutenin forms
"gluten."

Hordein, " " barley.

Zein, " " corn.

1E-1G. _Histones, Protamines and Albuminoids._--So far as is now known, no
representatives of these classes are found in plants.

2. Conjugated Proteins.--There is no conclusive evidence of the existence
in plants of any of the conjugated proteins, other than the nucleoproteins
and the chromoproteins, the composition and properties of which have been
discussed in previous chapters. The nucleoproteins undoubtedly occur in the
embryos of many, if not all, seeds.

3. Derived Proteins.--Representatives of the various types of derived
proteins are undoubtedly found as temporary intermediate products in
plants, both as products of hydrolysis produced during the germination of
seeds and as intermediate forms in the synthesis of proteins. So far as is
known, however, they do not occur as permanent forms in any plant tissues.
They have been prepared in large numbers and quantities, by the hydrolysis
of the natural proteins and the artificial synthesis of polypeptides.

In the present state of our knowledge concerning the functioning of the
proteins, no significance in the physiology of plant life, or metabolism,
is to be attached to the particular type of protein material which it
contains, at least so far as the simple proteins of the cytoplasm are
concerned.

DIFFERENCES BETWEEN PLANT AND ANIMAL PROTEINS

A much larger variety of protein materials is found in animal tissues than
in plants. This is undoubtedly because different animal organs perform so
much more varied physiological functions than do those of plants. Three
groups of simple proteins, the histones, the protamines, and the
albuminoids, which are quite common in animal tissues, are entirely unknown
in plants. Further, conjugated proteins of greater complexity and more
varied structure are found in animal tissues, especially in the brain,
nerve-cells, etc., than in plants.

Plant prot