I 



What are Animals and Plants f 38 1 



can receive them into a cavity, which is, to a certain extent, 

 comparable with the animal alimentary cavity, since that 

 is, morphologically, but an involution of the external 

 surface. 



4. Plants generally contain a greater amount of non- 

 nitrogenous material in their composition than do animals 

 generally, but this distinction is of little avail as regards the 

 lowest forms of life of both groups. 



5. Plants generally have a less evident power of forming 

 habits or of responding to stimuli by increased activity ; but 

 this again does not serve as a distinction as regards the lower 

 plants and animals. 



6. Until quite recently it could be said that no animals 

 possess that power of liberating carbonic acid and fixing 

 carbon which is possessed by plants; but now it is known 

 that certain worms also exercise this power. Nevertheless, 

 we may still say that plants generally possess the power of 

 feeding directly on the inorganic world and building up 

 organic matter from it, while the animal kingdom has it not ; 

 and this difference constitutes what is sometimes spoken of 

 as ' the circulation of the elements.' 



Until the other day it could have been said that with tho 

 exception of a loAvly species called ifnyxoimycetes, all plants 

 were organisms composed of one, few, or many small masses, 

 of protoplasm, separated from each other by partitions of a 

 non-nitrogenous substance called ' cellulose,' while in animals 

 the protoplasmic particles were not so separated. Quite 

 recently, however, it has been found that in some, and pro- 

 bably in very many if not in all plants, protoplasm is con- 

 tinuous, passing by minute filaments from cell to cell, 

 through such cellulose partitions. 



With the failure of this dfferential character, the very 

 last distinction between the two kingdoms, as ordinarily 

 understood, falls to the ground. We must profess ourselves 



