ANATOMY AND PHYSIOLOGY OF PLANTS. 251 



ported without the aid of nourishment, we therefore find, 

 that the root is an organ adapted for the absorption of 

 nutrient matter from the earth, from whence it is con- 

 veyed, in a somewhat altered state, to every part of the 

 plant, and constitutes its food or sap. 



From several experiments which have been tried to exhibit the 

 properties of sap, it is plain, it consists of a great variety ot ingre- 

 dients, differing in different species of plant ; but there is too little 

 known on the subject to establish any general conclusion. 



OF THE PROPER JUICE. 



3. In speaking of the structure of the leaf, we have 

 alluded to the course of the sap from the root upwards. 

 When it has received its gradual changes from the differ- 

 ent organs through which it has to pass, by the time it 

 passes the structure of the leaves, it is converted into 

 a peculiar fluid, called the proper juice. 



This fluid may be distinguished from the sap, by means of its 

 colour, which is generally green, as in the periwinkle ; or red, as in 

 logwood ; white, as in spurge ; or yellow, as in celandine. Its 

 principal seat is in the bark, where it occupies the proper tubes ; 

 but sometimes it is situated between the bark and wood, as in the 

 juniper tree ; or in the leaf, as in the greater part of herbs ; or it is 

 diffused throughout the whole plant, as in the fir and hemlock ; in 

 which case, either the proper juice mixes with the sap, or the vessels 

 containing it have ramifications which are so fine as not to be per- 

 ceptible. 



