THE PLANT BODY 19 



the more accurate plan of the stem, leaves, and branches. In 

 other herbaceous plants the lateral buds may all produce lateral 

 branches, and in that case the plant assumes a symmetrical 

 pyramidal or rhomboidal form like the ragweed (Ambrosia), 

 aster, and Russian thistle. All gradations in symmetry and reg- 

 ularity of form between the erect and the pyramidal or rhom- 

 boidal types mentioned occur in herbaceous plants, according to 

 the relation between the growth of the main axis and the later 

 branches. Where great irregularity in the growth of the lateral 

 branches occurs, the body plan is often obscured in the adult 

 plant but is evident in youth and in the arrangement of leaves 

 and buds on the branches. 



The form and development of trees. Among trees there is the 

 same general relation between the body plan, the growth of 

 buds and branches, and the ultimate form of the tree and its 

 adaptation to the forces and materials of the environment as 

 we have noted above in herbaceous plants. 



THE ERECT TKEE TYPE 



The pines. In erect tree types like the common pine (Fig. 10) 

 the main axis terminates each season in a twig which bears the 

 buds for the next season's growth. These buds consist of a vig- 

 orous terminal bud, which continues the elongation of the axis, 

 and of from three to five vigorous lateral buds clustered at the 

 base of the terminal bud. The remaining buds of the terminal 

 twig are latent and rarely if ever grow into lateral branches. 



When spring arrives the vigorous apical bud elongates and 

 produces the terminal twig of the season with its spirally 

 arranged scale and needle leaves. Meanwhile the vigorous lat- 

 eral buds elongate and produce a whorl of branches which are 

 separated from each other by inconspicuous internodes. Since 

 these branches arise from buds which are really arranged spirally 

 in the axils of minute scale leaves, they are called false whorls, 

 to distinguish them from true whorls, which could only arise on 

 trees with a cyclic body plan. The newest false whorl of each 

 season is separated from the false whorl of the previous season, 



