418 GROWTH OF THE SEED. 



office of depositing alburnous or woody matter; and 

 as soon as this is formed, the sap, which had hitherto 

 descended only through the cortical vessels, begins 

 to ascend through the alburnum. The plumule, in 

 consequence, elongates, its leaves enlarge and unfold, 

 and a set of vessels which did not exist in the root 

 are now brought into action. These, which I have 

 called the central vessels, surround the medulla, and 

 between it and the bark form a circle, upon which 

 the alburnum is deposited by the bark in the form 

 of wedges, or like the stones of an arch. Through 

 these vessels, which diverge into the leaf-stalks, the 

 sap ascends, and is dispensed through the vessels 

 and parenchymatous substance of the leaf; and in 

 this organ the fluid, recently absorbed from the soil, 

 becomes converted into the sap, or blood of the 

 plant: and as this fluid, during germination, de- 

 scended from the cotyledons and seed-leaves of the 

 plant, it now descends from its proper leaves, and 

 adds in its course to the bulk of the stem and the 

 growth of the roots. Alburnum is also deposited 

 in the stem of the plant, below the proper leaves, as 

 it was previously below the seed-leaves ; and from 

 this spring other ascending vessels, which give ex- 

 istence to, and feed, other leaves and buds." 



