18 



GENERAL BOTANY 



roots usually arise in an orderly succession, but there are no 

 definite nodes and internodes. We shall learn later that the 

 successful distribution of roots in the soil is determined in 

 most plants more largely by their powers of adjustment through 

 growth movements than by their arrangement on any fixed body 



plan. The relation of the 



body plan of aerial plant 

 parts to the ultimate form 

 of some common herbaceous 

 and woody plants will now 

 be considered. 



The form and development 

 of herbaceous plants. In a 

 number of herbaceous plants 

 the terminal bud grows rap- 

 idly during the early part of 

 the season and produces a 

 stout central stem, while the 

 lateral buds remain dormant 

 and thus fail to produce lat- 

 eral branches to any consid- 

 erable extent. The leaves 

 FIG. 9. Body plan and pyramidal form spring from the nodes either 

 of an herbaceous plant 



The ultimate form of this cineraria plant 

 and the exposure of its leaves to light are de- 

 termined largely by its spiral body plan, the 

 alternation of nodes and internodes, and the 

 continued growth of the terminal bud. Pho- 

 tograph by Fuller, from Cowles's " Ecology " 



in spiral or in cyclic order, 

 the lower leaves being usu- 

 ally somewhat larger and hav- 

 ing longer petioles than the 

 upper and younger ones. The 

 result of such growth is a 

 plant of pyramidal form (Fig. 9), in which the entire leafage 

 is admirably exposed to sunlight. 



The root system of such plants is variously arranged, but 

 without the definite plan of the aerial parts, owing to the fact 

 that the main root has no definite nodes from which lateral 

 roots spring. Since, however, the soil salts and water are usu- 

 ally distributed equally on all sides of the r6ots, and since there 

 is no danger from shading, it is evident that roots do not need 



