the action of each individual vegetative factor. We call these limits the 

 minimum and maximum and the degree of functioning at which a life pro- 

 cess most favors the development of the organism the optimum. 



The field of oscillation of the functions about the optimum, within the 

 limits promoting development may be called the "latitude of health." This 

 should not be confused with "the latitude of life" for the organism can still 

 live outside the latitude of health, but its functions are so weakened that its 

 development undergoes arrest or retrogression and this condition is disease. 

 If this cessation of the function is temporary, the condition falls under the 

 conception of "check" and we speak of check from cold or from darkness, 

 etc. But we must guard against the belief that the appearance of sickness 

 or a condition of check or of death in any species is connected with any pre- 

 cise numerical values for the separate factors of growth. If, for example, 

 we take two cuttings from the same plant and cultivate them for some time in 

 sand sterilized by heat with the same quantity of food materials but keep one 

 cutting in a hot house and the other out of doors, in the end the two will 

 show a very different susceptibility to frost and other atmospheric factors. 

 The specimen grown in the hot house freezes more easily; that is, its mini- 

 mum for the maintaining of life is raised. Temperatures, at which the speci- 

 men grown in the open air remains within the latitude of health, arrest the 

 life processes of the hot house specimen. Experiments to determine- the 

 maximum and minimum of other factors of growth show very similar 

 variations so that we may arrive at the conclusion that for each habitat each 

 plant has its ozvn scale of needs, its oivn optimum, maximum and minimum 

 and therefore possesses its ozvn specific latitude of health. 



Further, the circumstance that the different functions are lost at dilTer- 

 ent times should be considered. If, for example, potato tubers are left for 

 some time at a temperature of about — i°C., it will be found that respiration 

 ceases sooner than the conversion of starch into sugar. This results in an 

 accumulation of sugar in the tuber which is called "turning sweet of the 

 potato." If the temperature is raised more slowly to possibly -\-io°C. the 

 stored sugar disappears through the increased activity of Ihe protoplasm and 

 respiration. If cucumbers, tobacco and other heat loving plants have to 

 withstand a temperature of -i-5° to 8°C. for some time, they show a yellow- 

 leaf condition, which disappears with continued increase of heat. The 

 plants do not die, but assimilation and growth are so suppressed that proces- 

 ses, such as the formation of gums, may be introduced, leading to the prema- 

 ture death of the individual. As in the preceding case of deficient heat, 

 deficiency in food materials or light, — in short, every decrease of any vege- 

 tative function, — so retards the normal direction of the functions that the in- 

 teraction of these for the purpose of a beneficial metabolism is misdirected. 

 Other combinations and functional directions (for example, fermentations) 

 are now produced, which initiate the ending of life prematurely. The same 

 effect will necessarily appear every time the maximum of any vegetative 

 factor is exceeded, or even approximated. 



