The Various Substances Made by Plants 127 



in which the elements, or atoms, of the molecule, must sum up to 



more than 15,000, or even, in some cases, more than 30,000. Many 



of these substances differ little from one another in properties, 



and moreover are readily convertible one into 



another; and the facts seem to indicate that 



these elaborate forms are really multiples (or 



polymers) of some simple protein molecule, 



built up in the same manner as are starch and 



cellulose from a simple carbohydrate molecule. 



Nor is it to be supposed that all of these sub- 



stances have each a separate meaning in the 



plant, though they may have; but many of 



them no doubt are simply manifestations of 



chemical individuality in the plant, as the 



forms of starch grains are manifestations of 



physical individuality. 



Several different groups of Proteins are recognized by chemists, 



of which I shall here mention, even though in little more than the 

 Homeric fashion, the more important. They 

 are, Albumins, substances like white of egg, 

 thinly spread through many plants: Globulins, 

 which form definite grains in some seeds like 

 Corn (figure 39), and beautiful crystals in Castor 

 Bean, Potato and some other plants (figure 40) : 

 Glutelins, typified by the familiar gluten of 



fl UI> wMch & VeS the aggluthlOSity to dough : 



FIG. 39. A cell, highly 

 magnified, from the 

 proteinaceous layer 

 just under the husk 

 of Corn, showing nu- 

 merous protein 

 grains interspersed 

 with a few starch 

 (larger) grains, all 

 embedded in living 

 protoplasm. 



interior of a Castor Prolamins especially distinctive of the seeds of 



Bean, showing the . . . , 



crystalline protein grams : N ucleo-proteins , containing phosphorus, 



of cells: Phosphoproteins (called also 



tur^rendered some- an d forming the chromosome substance of the 



what clearer by 

 treatment with re- 

 agents), embedded in albuminates) cheese-like materials found in 



living protoplasm. 



some seeds: Proteases and Peptones, very im- 

 portant because they are the soluble and diffusable proteins into 

 which the insoluble kinds are converted in digestion by the 



