2O8 PROCESS OF DEVELOPEMENT. CHAP. IV. 



SECTION II. 

 Composite Organs. 



THE elucidation of the developement of the Com- 

 posite Organs involves the discussion of the two 

 following topics t the formation of the annual plant, 

 and of the original shoot of the perennial ; and the 

 formation of the subsequent layers that are annually 

 added to tho perennial. 



SUBSECTION I. 



Annuals and Annual Shoots. If a perennial of a 

 year's growth is taken up in the beginning of winter 

 when the leaves, which are only temporary organs, 

 have fallen, it will be found to consist of a root and 

 trunk, surmounted by one or more buds. The root 

 is the radicle expanded into the form peculiar to the 

 species, but the trunk and buds have been generated 

 Section of in the process of vegetation. Let the root or trunk be 

 ex ' now taken and cut into two by means of a transverse 

 section, and it will be found to consist already of 

 bark, wood, and pith. The pith is spongy and succu- 

 lent, being an assemblage of hexagonal cells filled 

 with a limpid juice. The wood is tender and brittle, 

 being an assemblage of longitudinal tubes, or fibres, 

 forming in the aggregate a cylinder or circular layer 

 that invests the pith. The bark is soft and flexible, 

 being also an assemblage of tubes that form in their 



