220 PHYSIOGRAPHY. [chap. 



any animal will serve to illustrate the essential characters of 

 all plants and of all animals. Every one has seen a field of 

 peas, thronged with pigeons. The peas will serve very well 

 as examples of plants, and the pigeons as types of animals. 



The pea that may be extracted from a ripe peascod is a 

 living body, in which, however, the vital activities are, for the 

 time, almost quiescent. Within the thin skin which envelops 

 the pea, there is inclosed a perfect, though embryonic plant, 

 composed of a minute stem with its root and leaves ; of 

 which last, two, the cotyledons or seed-leaves, are so large and 

 solid that they make up the chief mass of the infant pea- 

 plant. 



Subjected to chemical analysis, the embryo plant yields 

 certain complex bodies, composed chiefly of carbon, hydro- 

 gen, oxygen, and nitrogen, which are known as protein com- 

 pounds.^ Besides these it contains fatty matters ; woody 

 substance (cellulose), sugar, and starch ; various salts of 

 potash, lime, iron, and other mineral matters, including a 

 considerable proportion of water. 



Examined with the naked eye, the soft substance of the 

 young plant appears to be almost homogeneous ; the appli- 

 cation of the microscope, however, shows that it is far from 

 being really so ; but that, on the contrary, it has a very 

 definite and regular structure. A delicate woody framework, 

 or skeleton, is excavated by innumerable small cavities, each 

 of which is filled by a semifluid matter, termed protoplasm^^ 

 just as the honey fills the waxen cells of a honeycomb. 

 Each mass of protoplasm, with its investing wooden wall, is 

 technically termed a cell; and, inasmuch as part of the proto- 

 plasm is distinguishable from the rest as a rounded nucleus, 



1 Protein, from irpwreuco, protnio, to have the first place. 

 * Protoplasm, from Trpwros, protos, first ; and vKafffna, plasma, forma- 

 tive matter. 



