Heat and Plants 



and goes on more rapidly at a higher than at a 

 lower temperature. A temperature of, say, 60° F. 

 would not, however, hasten the performance of any 

 one function to the same extent in all plants alike, nor 

 does the most efficient performance of the separate 

 functions in any one plant all occur at the one 

 temperature. The best temperature for a plant is 

 a compromise between the different temperatures 

 at which its several functions reach their most 

 efficient working, and it varies with different plants, 

 and with the same plant at different periods in 

 its Ufe. There are, unfortunately, no observable 

 characters by which one can tell what range of 

 temperatures wiU best suit a given plant, and only' 

 experience can decide, although indications may be 

 obtained by a knowledge of the distribution of the 

 plant and of its relationships. A higher or a lower 

 temperature than that which suits the plant best is 

 bound to produce ill effects in it. A very high 

 temperature (usually anything over about 140° F.) 

 causes death, so also does a low temperature ; but 

 whereas most plants die at about the same tempera- 

 ture in the upper range, some can bear a far greater 

 degree of cold than others. The exact degree will 

 depend partly upon the condition of the plant, but 

 very largely upon its nature. 



We turn now to the special work of the different 

 parts of the plant. The root has two general 

 functions. It absorbs the water required and certain 



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