BOOK II. GENERAL CONSIDERATIONS. 237 



the sap that it receives, and returns the superfluous portion 

 of it downwards through the bark to the root ; it also sends 

 fibres down between the medullary sheath and the bark, thus 

 forming the first stratum of wood in the new stem. During 

 these operations, while the plumule is ascending, its leaf form- 

 ing and acting, and the woody matter created by its descend- 

 ing, the cellular tissue of the stem is forming, and expanding 

 horizontally to make room for the new matter forced into it ; 

 so that developement is going on simultaneously both in 

 a horizontal and perpendicular direction. This process may 

 not inaptly be compared to that of weaving, the warp being 

 the perpendicular, and the weft the horizontal, formation. In 

 order to enable the leaf to perform its functions of aeration 

 completely, it is traversed by veins originating in the pith, and 

 has delicate pores (stomates), which communicate with a 

 highly complex pneumatic system that extends to almost 

 every part of the plant. 



Simultaneously with the descent of fibres downwards from 

 the leaf, the emission of young roots, and their increase by 

 addition to the cellular substance of their points, take place. 

 They thus are made to bear something like a definite propor- 

 tion to the leaves they have to support, and with which they 

 must of necessity be in direct communication. 



After the production of its first leaf by the plumule, others 

 are successively produced around the axis at its growing 

 point, all constructed alike, connected with the stem or axis 

 in the same manner, and performing precisely the same func- 

 tions as have been just described. At last the axis ceases to 

 lengthen ; the old leaves gradually fall off; the new leaves, 

 instead of expanding after their formation, retain their rudi- 

 mentary condition, harden, and fold over one another, so as 

 to be a protection to the delicate point of growth ; or, in 

 other words, become the scales of a bud. We have now a 

 shoot with a woody axis, and a distinct pith and bark ; and 

 of a more or less conical figure. At the axil of every leaf 

 a bud had been generated during the growth of the axis ; so 

 that the shoot, when deprived of its leaves, is covered from end 

 to end with little, symmetrically arranged, projecting points, 

 which are the buds. The cause of the figure of the perfect 



