4 Plant Life and Evolution 



positive evidence that this is not the case, and all 

 experimental work must necessarily be based upon 

 the assumption that living matter is subject to the 

 same laws that govern inorganic bodies. 



So far as can be demonstrated, all manifestation 

 of life is indissolubly associated with certain ex- 

 tremely complex " protei 1 " substances which never 

 occur except in living bodies, and which are the 

 basis of the protoplasm, or living substance, of all 

 plants and animals. 



The evidence as to the possibility of spontaneous 

 generation at the present time is entirely negative. 

 All of the alleged successful experiments in this 

 direction have been shown to be the result of er- 

 rors, and as yet no successful attempts have been 

 made to produce living matter by artificial means. 

 So far as we know at the present time, all living 

 things arise from preexisting ones by some form 

 of reproduction. It is, however, the general belief 

 of biologists, that at some remote period living mat- 

 ter arose from inorganic elements. The theory 

 that living germs were brought to the earth from 

 somewhere in space is not generally accepted; and 

 the criticism has been made of this view that, after 

 all, it does not explain the origin of life, but merely 

 the advent of life upon the earth. 



Probably the most important advance made in 

 recent years towards an understanding of the na- 

 ture of the most primitive forms of life, has resulted 

 from the study of certain bacteria, which both 



