22 VITAL ACTIONS. 



adventitious buds ; and, in such cases, they may be 

 employed for the purposes of propagation. There 

 is no rule by which the power of a plant to generate 

 such buds by its roots can be judged of; experiment 

 is therefore necessary, in all cases, to determine the 

 point. 



CHAPTBE III. 



GROWTH BY THE STEM. 



Origin of the Stem. — The growing Point. — Production 

 of Wood, Bark^ Pith, Medullary Rays. — Properties 

 of Sap-wood, Heart-wood, Liber, Rind, &c., — Nature 

 and Office of Leaf-buds. — Eivhryo-huds. — Bulbs. — 

 Conveyance of Sap, and its Nature. 



42. As soon as the root is fully in action, which is 

 shortly after it has begun to lengthen, the vitality of 

 the living point that exists at the bottom of the seed- 

 leaves is excited, and a stem begins to be formed. 

 At first the stem is a mere point of living matter, often 

 invisible to the eye, but sometimes partially develop- 

 ed ; in which latter case it is called the plumule. But, 

 as soon as nutritive matter is conveyed into it by the 

 nascent root, all its parts receive an impulse, which 

 forces them into a growth upwards ; what matter 

 already exists is distended, enlarged, and solidified ; 

 new matter is rapidly generated in all directions from 

 the vital centre, and, if it were not for the current 

 setting upwards from the root, it would possibly 



