THE PBOTOPLAST AS HOUSE-BUILDER 57 



(Mentha). Every cluster of cells has a work to do sometimes special 

 kinds of work, but usually generalized kinds." 



We would remark, further, that the reserve materials which we have 

 been considering (not the degradation- and by-products, but the nutritious 

 substances) fall naturally into two great divisions. The first division 

 comprises those substances which, like protoplasm, contain the elements 

 carbon, hydrogen, oxygen, nitrogen, sulphur, and perhaps, in- some cases, 

 phosphorus. They are essentially the plastic materials out of which the 

 protoplasm produces its wonderful transformations. Hence the name proteids 



Photo fit/] \_E. Step. 



Fia. 86. LIME (Tilia). 

 The flowers of the Common Lime are here shown with their remarkable leafy bracts. EUROPE. 



has been bestowed upon them, from Proteus, the fabulous old man of the 

 sea, who possessed the remarkable power of changing his form. The 

 substances comprised under the second division are distinguished from pro- 

 teids by the absence of nitrogen and sulphur, whence they are frequently 

 called the non-nitrogenous compounds. 



The proteids include such substances as gluten, which forms a great part 

 of the corn-grains, and which is identical in its composition with albumen, 

 the basis of animal tissues ; legumin, which exists largely in the pea and 

 bean; and aleurow^-grains, which are abundant in oily seeds, and which 

 almost always enclose other bodies namely, crystalloids and globoids 



