PLANTS AND ANIMALS 221 



Animals are organisms possessing a nitro- 

 genous investment. 



These characters hold good for the active 

 individual only, and have no necessar^^ appli- 

 cation to reproductive stages. They are diag- 

 nostic characters and are not to be considered 

 as in anywise defining the powers or func- 

 tions of the two classes. 



In cellular organisms the investment may 

 extend to each protoplasmic unit, as is usual 

 in plants, or to the units of certain tissues, as 

 is usual in animals, or be developed only upon 

 the general exterior, as is specially the case in 

 coenocytic organisms, like some of the com- 

 mon molds and sea- weeds (Mucorin^ and 

 Siphonaceae) . 



By designating the constitution of the pro- 

 tective investment, it is intended to cover 

 only the original or basic substance of which 

 it is composed, without reference to subse- 

 quent depositions or infiltrations, of w^hat- 

 ever character they may be. Thus in the 

 walls of grasses and Equiseti there is often a 

 great amount of silica, in certain seaweeds 

 {Corallina) much lime, in tunicates so much 

 cellulose that it sometimes amounts to one- 

 fourth of the dry w^eight, and yet, in the case 

 of the plants named, the original and funda- 



