CH. VIII.] THE DISEASES OF PL^^'TS. 251 



animal frame, supplying noimshment and warmth to 

 all the parts, and where, by those being abstracted, 

 it is again converted into purple or venous blood, and 

 is returned by the veins to imdergo a repetition of 

 those changes already noted as being effected in the 

 lungs. In plants the sap, after exposure to the ac- 

 tion of the air in their leaves, is returned by another 

 set of vessels, situated in the bark, ministering to 

 the growth and support of the whole plant. It is 

 true, that only under certain circumstances, detailed 

 in another chapter, is heat evolved duiing the pro- 

 cesses of vegetation ; but the cumulation of the sap in 

 plants, beyond all doubt, enables them to resist the 

 intense colds and heats of their native chmates. In 

 frosts, the most intense and prolonged, we find the 

 interior of trees remain unfrozen ; and, under the 

 meridian sun of the tropics, the sap of the palm and 

 all other trees retain temperate coolness. This power 

 to resist extremely elevated and depressed tempera- 

 tures is characteristic of all animated nature. 



Such is the close similarity in the digestive and 

 circulatory processes characterising the members of 

 the two great kingdoms of organized nature, a resem- 

 blance which obtains in all the other functions en- 

 joyed by them in common. During respiration, the 

 air inhaled by animals through the mouth and nos- 

 trils proceeds immediately to the lungs, and acts 

 upon the blood ; in plants, the air inhaled by their 



