144 Temperature 



Methods of Meeting Temperature Extremes 



A surprising number of plants and animals can withstand consider- 

 able thermal fluctuation but do not possess any special mechanism for 

 meeting the problem of temperature extremes. When the ther- 

 mometer rises too high or drops too low, these animals and plants 

 must either "take it" or die. This is the situation for most sessile 

 aquatic invertebrates, for many other invertebrates, for many plants, 

 and for some higher animals. As we have seen, getting along without a 

 special temperature adaptation is easily possible for many organisms in 

 the aquatic environment. On land, however, north and south of the 

 killing frost line, and in areas exposed to intense heat, something must 

 be done to survive periods when the temperature exceeds the effec- 

 tive range within which active life can be maintained. 



Morphological and Physiological Adaptations. During the course 

 of evolution many specialized structures have been developed that 

 relate to the temperature problem. Certain animals and plants pro- 

 duce spores, cysts, eggs, pupae, or seeds that are capable of resisting 

 thermal extremes. Each of these structures represents a whole organ- 

 ism. In other species special parts of the fully developed organism 

 are resistant to extremes of heat and cold. Such is the situation with 

 the hardy roots and stems of many perennial plants. For example, 

 the tops of grass plants freeze off in winter. Life remains in the 

 stolons and roots of the grass, and from these organs new leaves are 

 produced when warm weather again returns. 



TABLE 8 



Temperature Relations of the House Fly, Musca domestica 



Death 46 . 5°C in few minutes Maximum survival temperature 



Heat coma 44 . 6 



Excessive activity 40 . 1 



Rapid movement 27 . 9 '\ Maximum effective temperature 



f 23 I . 



Normal activity ^ , _ > Effective temperature range 



Feeble movement 10.8 / Minimum effective temperature 



Begins moving 6.7 



Chill coma 6.0 



Death — 5.0 in 40 minutes Minimum survival temperature 



— 8.0 in 20 minutes Minimum survival temperature 



— 12.0 in 5 minutes Minimum survival temperature 



In some species physiological changes take place in the tissues that 

 prevent freezing. Osmotic concentration is increased, and water is 



