III. INFLUENCE OF CHEMICALS UPON PLANTS 



56. General Chemical Relations of the Organism. An analy- 

 sis of any mass of protoplasts reveals the invariable presence of 

 twelve of the known elements, and of one or two others in certain 

 organisms. Carbon, hydrogen, oxygen, and nitrogen are un- 

 doubtedly of the greatest importance to the cell so far as physio- 

 logical performance and structural value may be estimated. The 

 other elements may not actually enter into the plexus constituting 

 the living substance, yet it is absolutely necessary that their com- 

 pounds should saturate it in some form, and interlock in the special 

 cases of metabolism in which each one is a minor, though neces- 

 sary factor. The special part of each of the elements in the up- 

 building and growth of the body will form the subject of a section 

 on nutrition. 



Organisms sustain tonic or trophic relations to the indispen- 

 sable substances, and the three critical points may be distinguished 

 in the varying intensities in which they may act upon living mat- 

 ter. In addition, the trophic or nutritive elements, as well as 

 others to which protoplasm is totally foreign, exercise an irritable 

 influence. The non-trophic elements need be present in a certain 

 amount or intensity constituting the threshold of stimulation, in 

 order to affect living matter in such manner as to secure a re- 

 sponse, and a continuation of this intensity, unless the action is 

 injurious will generally be followed by an acclimatization, or ac- 

 commodation. Extensive increase of the intensity of a foreign 

 element, or compound, may produce rigor and tetanus, and prob- 

 ably injuries resulting in disorganization and death. 



The contact of a chemical compound may exercise a purely 

 chemical effect by modifying the molecular motion of the sub- 

 stances within the circle of living matter, by satisfying, or setting 

 free chemical affinities, thus modifying the performance of the 



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