26 THE TREES OF AMERICA. 



many instances be traced to this cause. There is no doubt that want of 

 proper and sufficient food may, and often does, produce similar results. If a 

 plant be deprived of its proper food, of course, like an animal under the same 

 condition, it cannot grow, or develop its vital heat, and blight and death must 

 follow; but I think that I have sufficient proof to show that blight and 

 kindred diseases are much more frequently produced in this manner than in 

 any other. Mr. Tudor's experiments seem to show this conclusively. Nothing 

 that he plants on bleak Nahant fails to grow, when protected from the full 

 force of the winds. In order to a proper understanding of this theory, how- 

 ever, we must examine somewhat more fully the process of the elimination of 

 vital heat by plants. 



The fact that all parts of growing plants eliminate vital heat is established 

 beyond a doubt, says Carpenter, and even, as the author himself has proved by 

 repeated experiments, during winter, when they are generally supposed to be in a 

 quiescent state. Indeed the production of vital heat seems to be necessary to 

 organized existence, however low in the scale it may rank ; but it is during the 

 process of flowering that its evolution is carried to the highest point. The 

 geranium, during this process, has shown an elevation of temperature of 6° 

 above that of the surrounding atmosphere. In the Arum tribe, where the 

 flowers are collected in great numbers, in cases which act as non-conductors, 

 this elevation of temperature is best shown. In one instance, where five 

 spadixes, of the Arum cordifolium, were made the subject of experiment, the 

 thermometer being placed in -the midst of them, it rose to 111°; in another, 

 where twelve spadixes were used, it rose to 121° ; the temperature of the exter- 

 nal air, in both cases, being but 66°. 



In considering this law of vegetable existence in its relation to blight and other 

 diseases, it will be seen at once that plants, like animals, can of course supply 

 only a definite amount of heat during a given period of time ; and if more is 

 demanded from any cause, injury must follow in proportion to the character and 

 condition of the plant, and the increased demand made upon its vital power. 

 If, for instance, a plant is capable of supplying a definite amount of heat to the 

 passing breeze, say 60°, during ten minutes, and the wind be increased in violence 



