184 Eff^^^'^ of Frost on Dormant Vegetation. [^li^YW.^ 



rapidity with wliicli their fluids circulate. 4th. The liability to freeze, 

 of the fluids contained in the plants, is greater in proportion to the size 

 of the cells. 5 th. The power of plants to resist extremes of temperature, 

 is in direct proportion to the quantity of confined air which the structure 

 of their organization gives the means of retaining in the more delicate 

 parts. 6th. The power of plants to resist extremes of temperature, is 

 in direct proportion to the capability which the roots possess of absorbing 

 sap, less exposed to the external influence of the atmosphere and the 

 Bun." 



Taking the above statements for granted, we shall have to ask the 

 question, By what agency are plants enabled to resist cold at all ? This 

 important question has given rise to many controversies. For a long 

 time the opinions of persons skilled in vegetable physiology have been 

 divided touching this point. By some it was claimed that vegetable 

 life is supported and protected by a certain degree of warmth generated 

 within the plant itself, similar to the generation of heat in the animal 

 economy. This doctrine seems to have been received, in a former period 

 in the history of natural science, as an axiom in vegetable physiology. 

 Having been founded on given causes and supposed facts which could not 

 stand the test of closer observations and more rigid analyses, this doc- 

 trine was subsequently rejected, and finally abandoned, like many other 

 attempts to establish philosophic theories upon supposed parallels and 

 resemblances in the functions of animal and vegetable life. 



In close connection with this doctrine of an independent vegetable heat, 

 of former years, we find the strange opinion prevailing, about the same 

 period, that freezing the fluids of the plant would most certainly prove 

 destructive to its life and well being. This idea is plainly contradicted 

 by every winter day's experience ; though it is true that the fluids of 

 many plants are found to freeze and so remain for a long time without 

 injury to their future germination and growth. Various other proofs 

 were presented by the advocates of an independent vegetable heat, to 

 sustain its doubted existence. It was stated that a higher degree of heat 

 is required to congeal the fluids of a plant, than is necessary to freeze 

 ordinary water. Ice was found to melt when brought into contact with 

 living plants ; and the interior of trees showed a higher temperature 

 than the surrounding atmosphere. 



In relation to the first of these statements — that a greater degree of 

 cold is required to freeze the contents of a plant than common water, the 

 fact is clearly accounted for, by simple laws of physics, without any 

 appeal to vegetable organism ; if so, it is in no wise to be received as a 

 proof of heat, inherent in the plant as such. Dr. Lindley, speaking of 



