45(3 CHARACTER OF VEGETABLE VITALITY. CHAP. XI. 



Though it Hence it follows that even during the period of 



is roused ... ,, , 



into in- winter, when vegetation seems totally at a stand, 



" the tree being stripped of its foliage, and the herb 

 the spring. a pp arent ] v withering in the frozen blast, still the 

 energies of vegetable life are exerted ; and still the 

 vital principle is at work, carrying on in the interior 

 of the plant, concealed from human view, and shel- 

 tered from the piercing frosts, operations necessary 

 to the preservation of vegetable life, or protrusion 

 of future parts ; though it requires the returning 

 warmth of spring to give that degree of velocity to 

 the juices which shall render their motion cognizable 

 to man, as well as that expression to the whole 

 plant which is the most evident token of life : in the 

 same manner as the processes of respiration, diges- 

 tion, and the circulation of the blood are carried on 

 in the animal subject even while asleep ; though the 

 most obvious indications of animal life are those of 

 the motions of the animal when awake. 

 Bythesti- Heat then acts as a powerful stimulus to the 

 heat. operations of the vital principle, accelerating the 

 motion of the sap, and consequent developement 

 of parts ; as is evident from the sap's beginning to 

 flow much more copiously as the warmth of spring 

 advances, as well as from the possibility of antici- 

 pating the natural period of their developement by 

 forcing them in a hot-house. But it is known that 

 excessive heat impedes the progress of vegetation as 

 well as excessive cold ; both extremes being equally 

 prejudicial. Arid hence the sap flows more copiously 



